Free KCSE Physics Topical Questions KNEC Standards

A 240v mains transformer has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp

21/10/2021

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(a) A 240v mains transformer has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp.

(i) Calculate the number of turns in the secondary (2mks)

(ii) What is the efficiency of the transformer if the current drawn from the 240V mains is 100mA (2mks)

The circuit above shows a step-down transformer used to light a lamp of resistance.

Calculate.

(i) the reading of voltmeter, V, with, S, open (2mks)

(ii) the reading of the ammeter A with S closed (neglect the effective resistance of the secondary winding) (2mks)

(iii) the power dissipated in the lamp (2mks)

(iv) the primary current if the transformer is 90% efficient (3mks)

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Complete the figure below to show how a single pulley can be arranged to a velocity ratio(V.R) of 2

16/10/2021

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Complete the figure below to show how a single pulley can be arranged to a velocity ratio(V.R) of 2 (2mks)

Complete the figure below to show how a single pulley can be arranged to a velocity ratio(V.R) of 2

Solved ...

a single pulley arranged to a velocity ratio(V.R) of 2

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K.C.S.E Physics Q & A - MODEL 2019PP1QN15

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP1QN15

(a)Figure 6 shows n bottle top opener being used to open a bottle.

Indicate on the diagram the direction of the load and the effort.
(b) State two ways ¡n which an inclined plane can be made to reduce the applied effort when pulling a Load along the plane.
(c) A block and tackle system has three pulleys in the upper fixed block and two pulleys in the lower movable block.
(i) Draw a diagram to show how the system can be set up in order to lift a load arid indicate the position of the load and effort.
(ii) State the velocity ratio of the set up.
(iii) In such a block and tackle system an effort of 200N is required to lift a load of 600N. Determine its efficiency

answers

(b)Reducing the angle of inclination.
Reducing the friction — using rollers, lubricants etc.

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K.C.S.E Physics Q & A - MODEL 2018PP1QN16

29/7/2020

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K.C.S.E Physics Q & A - MODEL 2018PP1QN16

(a) An electric crane uses 8.0 x10⁴ N of energy to lift a load of 2.0 X 10⁴N in 4s.
(i) Determine the;
I power developed by the crane,
II height to which the load is lifted,
III efficiency of the crane whose motor is rated 2.5 X 10⁴ W.
(ii) State two forms of energy transformation that lead to the crane’s inefficiency.
(b) A stone is dropped from the top of a building to the ground. On the axes provided, sketch a graph of potential energy against time for the stone.

answers

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K.C.S.E Physics Q & A - MODEL 2016PP1QN16

27/7/2020

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K.C.S.E Physics Q & A - MODEL 2016PP1QN16

(a)Define the term velocity ratio of a machine.
(b) Fig. 12 shows part of a hydraulic press. The plunger is the position where effort is applied while the Ram piston is the position where load is applied. The plunger has cross-section area, a m² while the Ram piston has cross-section area, A m².

When the plunger moves down a distance d the Ram piston moves up a distance D.
Derive an impression for the velocity ratio (V.R) in terms of A and a
c) A machine of velocity ratio 45, overcomes a load of 4.5 x 10³N when an effort of 135N is applied. Determine:
(i)The mechanical advantage of the machine;
(ii) Efficiency of the machine;
(iii) The percentage of the work that goes to waste.

answers

(a)It is the ratio of distance moved by effort to distance moved by load

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K.C.S.E Physics Q & A - MODEL 2015PP1QN15

24/7/2020

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K.C.S.E Physics Q & A - MODEL 2015PP1QN15

(a) Figure 8 shows a 200 g mass placed on a frictionless surface and attached to a spring.

The spring is compressed and released. Given that the elastic potential energy of the compressed spring is 2.7 X 10^-2 J, determine the maximum speed with which the block moves after it is released.
(b) In a wheel and axle system, state the advantage of having a large wheel diameter compared to the axle diameter for a frictionless system.
(c) A body is released from a height h. Sketch a graph of potential energy against kinetic energy as the body falls to the ground.
(d) Figure 9 shows a hydraulic lift system. The radius of the small piston is 3 cm while that of the larger piston is 9 cm. A force of 90 N is applied to the smaller piston.

Determine the:
(i) maximum load that can be lifted.
(ii) efficiency of the system.

answers

(b)(b) Reduces the effort required to raise the 1oad (increases the mechanical advantage.)

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K.C.S.E Physics Q & A - MODEL 2014PP1QN16

23/7/2020

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K.C.S.E Physics Q & A - MODEL 2014PP1QN16

Figure 10 shows a trolley of weight 20 N pulled by a force of 4 N from the bottom to the top of an inclined plane at a uniform speed.

(a) (i) State the value of the force acting downwards along the inclined plane.
(ii) Explain how the value in part (a) (i) is obtained.
(b) For the system. determine the:
(i) mechanical advantage;
(ii) velocity ratio;
(iii) efficiency.

answers

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K.C.S.E Physics Q & A - MODEL 2013PP1QN16

22/7/2020

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K.C.S.E Physics Q & A - MODEL 2013PP1QN16

(a) A horizontal force of 12 N is applied on a wooden block of mass 2 kg placed on a horizontal surface. It causes the block to accelerate at 5 m/s2. Determine the frictional force between the block and the surface. (3 marks)
(b) Figure 9 shows a graph of velocity against time for a ball bearing released at the surface of viscous liquid.

Explain the motion of the ball bearing for parts
(I) OA
(ii) AB
(c) Figure 10 shows a pulley system used to raise a load by applying an effort of 500 N.

State the:
(i) velocity ratio of the system.
(ii) purpose of pulley 2.
(iii) Given that the machine has an efficiency of 80%, determine the maximum load that can be raised.

answers

(b) (I) OA - the ball bearing decelerates; as the upthrust increases to a maximum;
AB - baIl attains terminal velocity; when upthrust = weight;

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State two reasons why the efficiency of a pulley system is always less than 100%.

21/7/2020

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K.C.S.E Physics Q & A - MODEL 2012PP1QN12

State two reasons why the efficiency of a pulley system is always less than 100%.

answer

Friction between the moving parts o(the pulley system;
Work done against friction;
Work done lifting the moving parts of the pulley system;

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K.C.S.E Physics Q & A - MODEL 2010PP1QN15

19/7/2020

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K.C.S.E Physics Q & A - MODEL 2010PP1QN15

(a) A cyclist initially at rest moved down a hill without pedaling. He applied brakes and eventually stopped. State the energy changes as the cyclist moved down the hill.
(b) Figure 7 shows a mass of 30kg being pulled from point P to point Q, with a force of 200N parallel to an inclined plane. The distance between P and Q is 225m. In being moved from P to Q the mass is raised through a vertical height of 75m.
(i) Determine the work done:

I by the force;
II on the mass;
III to overcome friction.
(ii) Determine the efficiency of the inclined plane.
(c) Suggest one method of improving the efficiency of an inclined plane

answers

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K.C.S.E Physics Q & A - MODEL 2009PP1QN16

17/7/2020

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K.C.S.E Physics Q & A - MODEL 2009PP1QN16

(a) Define the term efficiency of a machine
(b) Figure 9 shows a drum of mass 90 kg being rolled up a plane inclined at 25⁰to the horizontal. The force F applied is 420N and the distance moved by the drum along the plane is 5.2 m

Determine:
(i) The work done by the effort
(ii) The work done in raising the drum
(iii) The efficiency of the inclined plane as a machine

answers

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K.C.S.E Physics Q & A - MODEL 2008PP1QN18

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP1QN18

(a) Define the term velocity ratio of a machine.
(b) Fig. 12 shows part of a hydraulic press. The plunger is the position where effort is applied while the Ram piston is the position where load is applied. The plunger has cross-section area, a m2 while the Ram piston has cross-section area, a m2.

When the plunger moves down a distance d the Ram piston moves up a distance D.
(i) State the property of liquid pressure on which the working of the hydraulic press works.
(ii) Derive an impression for the velocity ratio (V.R) in terms of A and a.
c) A machine of velocity ratio 45, overcomes a load of 4.5 x 103N when an effort of 135N is applied.
Determine:
(i) The mechanical advantage of the machine;
(ii) Efficiency of the machine;
(iii) The percentage of the work that goes to waste.

answers

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K.C.S.E Physics Q & A - MODEL 2008PP1QN03

15/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP1QN03

Fig. 1 shows a brick placed on a plane inclined at an angle to the horizontal. The weight, W, of the brick is shown.

a) On the same diagram show with arrows the other two forces acting on the brick and name them.
b) State how each of the two forces named (a) above is affected when the angle is reduced.

answer

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K.C.S.E Physics Q & A - MODEL 2006PP1QN07

14/7/2020

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K.C.S.E Physics Q & A - MODEL 2006PP1QN07

Figure 5 shows two pulleys systems being used to raise different loads. The pulleys identical.

State one reason why system B may have a higher efficiency than system A.

answer

Effect of weight of second pulley reduces efficiency of A. Load in B is larger and so effect of friction is less in B increasing efficiency.

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K.C.S.E Physics Q & A - MODEL 2005PP2QN02

13/7/2020

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K.C.S.E Physics Q & A - MODEL 2005PP2QN02

a) Fig 2. Shows a wheel and axle being used to raise a load W by applying an effort F The radius of the large wheel is R and of the small wheel r as shown.

(i) Shows that the velocity ratio (V.R) of this machine is given by R/r
(ii) Given that r= 5cm, r=8cm, determine effort required to raise a load of 20N if the efficiency of the machine is 80%
(iii) It is observed that the efficiency of the machine increases when it is used to lift large loads. Give a reason for this.

answers

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A certain machine uses an effort of 400N to raise a load of 600N. If the efficiency of the machine is 75%, determine its velocity ratio.

13/7/2020

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K.C.S.E Physics Q & A - MODEL 2005PP1QN15

A certain machine uses an effort of 400N to raise a load of 600N. If the efficiency of the machine is 75%, determine its velocity ratio.

answer

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K.C.S.E Physics Q & A - MODEL 2004PP1QN18

12/7/2020

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K.C.S.E Physics Q & A - MODEL 2004PP1QN18

A body of mass 60kg is pulled at a uniform velocity up smooth inclined surface as shown in Figure 1

If the distance moves along the incline is 4.0m, determine work done by the force F.

answer

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K.C.S.E Physics Q & A - MODEL 2003PP2QN02

12/7/2020

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K.C.S.E Physics Q & A - MODEL 2003PP2QN02

a) A crane lifts a load of 200kg through a vertical distance of 3.0m in 6 seconds.
Determine:
(i) Work done
(ii) Power development by the crane.
(iii) Efficiency of the crane given that it is operated by an electric motor rated 12.5kW.
(b) A child of mass 20kg sits on a swing of length 4m and swings through a vertical height of 0.9m as shown in figure 2.

Determine:
(i) Speed of the child when passing through the lowest point.
(ii) Force exerted on the child by the seat of swing when passing through the lowest point.

ANSWERS

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K.C.S.E Physics Q & A - MODEL 2002PP2QN03

10/7/2020

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K.C.S.E Physics Q & A - MODEL 2002PP2QN03

Fig. 4 shows a block of a mass 30.0 kg being pulled up a slope by a force P at a constant speed. The friction force on the block is 20.0N

a i) On the same figure name and indicate the other forces acting on the block.
ii) Determine the component of the weight acting on the trolley down the slope
iii) Determine the value of P.
b) On reaching the top of the slope, the block is left to run freely down the slope.
i) Which one of the forces previously acting on the block would then act in the opposite?
ii) Determine the acceleration of the block down the slope.
iii) What is the effect of increasing the angle of slope on your answer in (ii) above.

answers

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K.C.S.E Physics Q & A - MODEL 2002PP1QN15

10/7/2020

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K.C.S.E Physics Q & A - MODEL 2002PP1QN15

Fig. 10 shows how the potential energy, (P.E) of a ball thrown vertically upwards, varies with height.

Determine the distance the car travels in the first 40 seconds.

On the same axes, plot a graph of the kinetic energy of the ball.

answer

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K.C.S.E Physics Q & A - MODEL 2001PP1QN15

9/7/2020

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K.C.S.E Physics Q & A - MODEL 2001PP1QN15

A certain machine raises 2.0 tonnes of water through 22 metres.It the efficiency of the machine is 80%, how much work is done on the machine.(Acceleration due to gravity g = 10ms^-2)

answer

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K.C.S.E Physics Q & A - MODEL 2000PP1QN15&16

8/7/2020

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K.C.S.E Physics Q & A - MODEL 2000PP1QN15&16

Fig 10 shows a pulley system being used to raise a load. Use the information given in the figure to answer the questions 15 and 16.

Determine the velocity ratio (VR) of the system.
If a load on 100N is raised by applying an effort of 28N, determine the efficiency of the system

ANSWERS

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K.C.S.E Physics Q & A - MODEL 1999PP1QN16

7/7/2020

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K.C.S.E Physics Q & A - MODEL 1999PP1QN16

Figure 11 is a graph which shows how the vertical height through which a machine raises a mass 20kg varies with time.

Determine the power output of the machine after 40 seconds.

ANSWER

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(a) A 240v mains transformer has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp. ​

(i) Calculate the number of turns in the secondary (2mks)

(ii) What is the efficiency of the transformer if the current drawn from the 240V mains is 100mA (2mks)

​Calculate.

(i) the reading of voltmeter, V, with, S, open (2mks)

(ii) the reading of the ammeter A with S closed (neglect the effective resistance of the secondary winding) (2mks)

(iii) the power dissipated in the lamp (2mks)

(iv) the primary current if the transformer is 90% efficient (3mks)

Complete the figure below to show how a single pulley can be arranged to a velocity ratio(V.R) of 2 (2mks)

Solved ...

K.C.S.E Physics Q & A - MODEL 2019PP1QN15

K.C.S.E Physics Q & A - MODEL 2018PP1QN16

K.C.S.E Physics Q & A - MODEL 2016PP1QN16

(a)Define the term velocity ratio of a machine. (b) Fig. 12 shows part of a hydraulic press. The plunger is the position where effort is applied while the Ram piston is the position where load is applied. The plunger has cross-section area, a m2 while the Ram piston has cross-section area, A m2.

K.C.S.E Physics Q & A - MODEL 2015PP1QN15

K.C.S.E Physics Q & A - MODEL 2014PP1QN16

K.C.S.E Physics Q & A - MODEL 2013PP1QN16

State two reasons why the efficiency of a pulley system is always less than 100%.

K.C.S.E Physics Q & A - MODEL 2010PP1QN15

K.C.S.E Physics Q & A - MODEL 2009PP1QN16

(a) Define the term efficiency of a machine (b) Figure 9 shows a drum of mass 90 kg being rolled up a plane inclined at 250to the horizontal. The force F applied is 420N and the distance moved by the drum along the plane is 5.2 m

K.C.S.E Physics Q & A - MODEL 2008PP1QN18

K.C.S.E Physics Q & A - MODEL 2008PP1QN03

K.C.S.E Physics Q & A - MODEL 2006PP1QN07

K.C.S.E Physics Q & A - MODEL 2005PP2QN02

A certain machine uses an effort of 400N to raise a load of 600N. If the efficiency of the machine is 75%, determine its velocity ratio.

K.C.S.E Physics Q & A - MODEL 2004PP1QN18

K.C.S.E Physics Q & A - MODEL 2003PP2QN02

K.C.S.E Physics Q & A - MODEL 2002PP2QN03

K.C.S.E Physics Q & A - MODEL 2002PP1QN15

K.C.S.E Physics Q & A - MODEL 2001PP1QN15

A certain machine raises 2.0 tonnes of water through 22 metres.It the efficiency of the machine is 80%, how much work is done on the machine.(Acceleration due to gravity g = 10ms-2)

K.C.S.E Physics Q & A - MODEL 2000PP1QN15&16

K.C.S.E Physics Q & A - MODEL 1999PP1QN16

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(a) A 240v mains transformer has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp.

Calculate.

(a)Define the term velocity ratio of a machine.
(b) Fig. 12 shows part of a hydraulic press. The plunger is the position where effort is applied while the Ram piston is the position where load is applied. The plunger has cross-section area, a m² while the Ram piston has cross-section area, A m².

(a) Define the term efficiency of a machine
(b) Figure 9 shows a drum of mass 90 kg being rolled up a plane inclined at 25⁰to the horizontal. The force F applied is 420N and the distance moved by the drum along the plane is 5.2 m

A certain machine raises 2.0 tonnes of water through 22 metres.It the efficiency of the machine is 80%, how much work is done on the machine.(Acceleration due to gravity g = 10ms^-2)