KCSE 2023 Physics Force Revision Questions, Answers

Force is the second topic in form one  Physics.

1. Define force and give its SI units

2. Name two effects of force
3. State the reason why it is not correct to quote the weight of solid objects

in kilograms                                                                          (1mk)

4. Name the type of force that:                                       (4mk)

• (i) Attracts bodies toward the centre of the earth.
• (ii) Opposes motion between two surfaces in contact.
• (iii) Makes an object appear lighter when being lifted out of water.
• (iv) Attracts pieces of papers to a plastic ruler when the ruler is rubbed on hair.
• (v) Enables a body to move in a circular motion

SURFACE TENSION

4. What is surface tension?  (1mk)
5. State two factors that lowers the surface tension force on a water surface.
6. State one way of making the surface tension of a liquid stronger. (1 mk)
7. State the effect of a decrease in temperature on surface tension. 1mk
8. A steel needle placed on water is found to float even though steel is denser than water. But when the water is heated the needle sinks.  Explain why.
9. Explain a metal pin was observed to float on the surface of pure water. However the pin sank when a few drops of soap solution were carefully added to the water.      (1mk)
10. Explain the washing effect of soap. (1mk)
11. If a tent is touched with a finger on inner surface, when it is raining, it allows the rain water to leak through. Give a reason for this observation. (1mk)
12. The diagram below shows a wire loop with two threads tied across it. The loop is dipped into a soap solution such that the soap film covers it as shown.

Region B is punctured such that the soap film in that section is broken. On the space alongside the diagram sketch the resulting shape of the wire loop. Give a reason for the shape.                                                                       (2mks)

10. The diagram below shows a wire loop with a thread tied across it. The loop is dipped into a soap solution such that the soap film covers it as shown.

Region X is punctured such that the soap film in that section is broken. On the space alongside the diagram sketch the resulting shape of the wire loop. Give a reason for the shape.                                                                       (2mk)

11. Figure shows a funnel dipped into a liquid soap solution.

State and explain what happens to the soap bubble when the funnel is removed.    (2mk)

12. A glass funnel is dipped in soap solution, then taken out and blown gently to form a soap bubble as shown below

Explain why the bubble flattens to a film which then rises up the funnel.

(2mks)

13. The figure below shows a small toy boat floating on water in a basin. X and Y are two point near the toy.

When a hot metal rod is dipped into the water at point X, the toy is observed to move towards Y.  Explain this observation.                                            2mk

14. The Figure below shows a toy boat. A piece of soap is attached to end A and then the toy placed on a surface of clean water.

               Explain the observation that would be made immediately.       (2mks)

ADHESIVE AND COHESIVE FORCE

1. Differentiate cohesive force from adhesive (2mk)

2. Anyango placed her finger on a water as shown in the diagram below

Name the force that lifts the water to the finger                                   (1mk)

3. Explain the reason why water spilled on a glass surface wets the surface.                                                                (1mk)
4. When building a house using bricks a damp course is laid just above the brick foundation.   Explain why the damp course is necessary (1mk)

5. Name two types of forces which can act between objects without contact.

6. Name two types of forces which can act between objects in contact.

7. Give a reason why lamp – wicks are usually made of cotton. (1mk)

8. The diagram below shows drop of liquids X and Y carefully put on a clean flat glass slab

Explain the shapes of the drops                                            (2mks)

9. Explain why you can dry your hands with a towel but not with a sheet of polythene (1mk)

10. When drops of water are sprinkled on a greasy glass plate they form spherical shapes. Explain.
11. Name two kinds forces that determine the shape of a liquid drop on solid surface.

12. State two factors which determine the height to which a liquid rises up a capillary tube If dipped into the liquid. (2 mk)

13. Explain the following observation. Rain drops falling freely are spherical                                                                     (1mk)
14. Fig shows the meniscus of water in a glass tube.

Explain why the meniscus of the liquid is shaped as shown.          2mk

15. The diagram below shows the behaviour of mercury in a capillary tube.

Explain the behaviour                                                                           2mk

16. The figures (a) and (b) below shows capillary tubes inserted in water and mercury respectively.

It is observed that in water the meniscus in the capillary tube is higher than the meniscus in the beaker, while in mercury the meniscus in the capillary tube is lower than the meniscus in the beaker. Explain these observations.(2mk)

17. The figures (i) and (ii) below shows two capillary tubes dipped in water and mercury respectively.

 Indicate on the diagrams above the likely levels of water and mercury in the respective tubes.                                                           (1mk)

1. Explain your answer in (i) (2mk)

18. The diagram below shows a capillary tube immersed in water.

Using figure (b) sketch to show the appearance of the capillary tube if it was inserted in mercury.

19. The diagram below shows two clear glass tubes containing water and mercury

Explain the shapes of the surface of each of the liquids inside the tube.  (2mk)

20. Figure a & b below shows narrow tubes dipped in mercury and water respectively.

The temperatures of the two liquids in the containers are raised slightly. Indicate the new  levels of mercury and water in the tubes respectively.    (1 mk)

21. Figure shows a narrow tube dipped in water.

The temperature of the liquid (water) is raised.  Indicate on the diagram the new level of water.  Explain your answer.                                                   (2mks)

MASS AND WEIGHT

1. State three differences between mass and weight.          (3mk)

2. State the reason why it is not correct to quote the weight of solid objects in kilograms                                                                     (1mk)

3. Differentiate vector quantity from a scalar quantity and give an example of each
4. Using a scale of 1cm to represent 10N, draw a diagram to show the direction and magnitude of the resultant force for two forces acting as shown below. (1mk)

5. Show diagrammatically how you can combine forces of:

• 9N, 7N and 2N to give a resultant force of 4 N                 (2mk)        

(b)   3N, 5N and 7N to give a resultant force of 15 N.              (2mk)           

6. Determine the resultant vector due to the forces below

(i)

(ii)

7. The fig (I) below shows a body acted on by two forces F₁=3N and F₂=8N

On the fig (II) below draw the force F₃ that has the same effect on the body as the two forces.                                                                     (2mk)

8. Show diagrammatically how you can combine forces of 9N and 2N to give a resultant force of
9. i) 7 N
10. ii) 11 N

9. Show diagrammatically how you can combine forces of:

• 9N, 7N and 2N to give a resultant force of 4 N
• 3N, 5N and 7N to give a resultant force of 15 N.

10. Show diagrammatically how you can combine forces of:12N, 7N and 5N to give a resultant force of

• (i) 24N
• (ii) 0N
• (iii) 14N
• (iv) 10N

11. Show diagrammatically how you can combine forces of:18N, 7N and 6N to give a resultant force of 15N                                (2mk)       
12. A student was heard saying “the mass of a ball on the moon is one sixth its mass on earth”. Give a reason why this statement is wrong.

13. The weight of a person increases as one move away from the equator towards the poles. Give a reason for this.
14. Give a reason why the weight of a body varies from place to place.
15. A bag of sand is found to have the same weight on planet earth as an identical bag of cotton on planet Jupiter. Explain why the masses of the two bags must be different.                                          (2mk)                                                           

16. Explain a bag of sugar is found to have the same weight on planet moon as an identical bag of dry saw dust on the earth. (1mk)
17. An astronaut weighs 800 N on earth where g=10N/kg. Calculate
18. i) His mass
19. ii) His weight on the moon where g=1.6N/kg
20. An astronaut weighs 800 N on mars where g=16N/kg.  Calculate
21. i) His mass
22. ii) His weight on Jupiter where g=20N/kg.
23. An object weighs 600 N on Earth. What would its weight be on another planet of gravitational acceleration 8 N/kg.
24. A body weighs 600N on the surface of the earth where g = 10N/Kg and 150N on the surface of Venus. Calculate the value force of gravity on Venus.
25. An astronaut weighs 1200 N on Jupiter which has gravitational strength of 20N/Kg. Calculate
26. His mass on Jupiter
27. His weight on the Earth.
28. The weight of a stone on the moon is found to be Determine its weight on earth given that the gravitational force on the moon is 1.6N/kg

23. An object weighs 0 N on Earth. What would its weight be on another planet of gravitational acceleration 6.25 N/kg given that acceleration due to gravity on earth is 9.8N/kg                                                                 (2mks)

24. The graph in the figure below shows the variation of the weights W of various objects with their respective masses,

.

Use the graph to determine the gravitational field strength.                  (3 mks)

SCHEEM

1. Explain the following observation;

Cohesive force in water molecules is high                                    1mk

2. Explain the washing effect of soap. (1mk)

Detergent lowers the surface tension of water making it stick to dirt and remove it. Ö1/Penetrate the space between dirt and fabric.

3. Give a reason why lamp – wicks are usually made of cotton. (1mk)

      Adhesive force between kerosene and cotton is higher than cohesive force

between kerosene molecules. ;

4. Name two kinds forces that determine the shape of a liquid drop on solid surface.

Adhesive√¹ and cohesive√¹ force.

5. Explain why you can dry your hands with a towel but not with a sheet of polythene (1mk)

The force of adhesion between water and the towel is higher than that between water and the polythene sheet;                                (1mk)

25. Give a reason why the weight of a body varies from place to place.

ANS Distances vary from the centre of earth  to different places hence the weight of a body on those different places vary ( 1mk)

Ans   Increase in temperature lower surface tension force;

26. Figure a & b below shows narrow tubes dipped in mercury and water respectively. The temperatures of the two liquids in the containers are raised slightly. Indicate the new levels of mercury and water in the tubes respectively.    (1 mk)