## 02 May 2011

### CBSE PHYSICS Force and law of motion Numerical for class 9

1. A boy is wearing a shirt of mass 150 g. How much force is he exerting on the dress? Do not forget to state the direction.

2. Your physics book has a mass of 400 g. It is kept on a horizontal table. Taking g = 10 m/s 2, find the force (both magnitude and direction) exerted by

(a) the table on the physics book

(b) the physics book on the table

(c) the earth on the physics book

(d) the physics book on the earth.

3. How much force is needed to produce an acceleration of 16 cm/s2 in a body of mass 250 g?

4. A force of 10 N acts on a particle of mass 0.4 kg. Find the acceleration of the particle.

5. A body of mass 1 kg is kept at rest. A constant force of 6.0 N starts acting on it. Find the time taken by the body to move through a distance of 12 m.

6. The velocity of a particle of mass 150 g changes from 8 m/s to 12 m/s in two seconds. Assuming that a constant force acts on it, find the magnitude of the force.

7. A force of 4.0 N acts on a body of mass 2.0 kg for 4.0 s. Assuming the body to be initially at rest, find

(a) its velocity when the force stops acting,

(b) the distance covered in 10 s after the force starts acting.

8. A coin of mass 20 g is pushed on a table. The coin starts moving at a speed of 25 cm/s and stops in 5 seconds. Find the force of friction exerted by the table on the coin.

9. When a body is dropped from a height, it falls with an acceleration of 10 m/s2. If its mass is 250 g, how much force is exerted on it downwards? Who exerts this force on the body?

10. A feather of mass 20 g is dropped from a height. It is found to fall down with a constant velocity. What is the net force acting on it?

11. When a horizontal force P acts on a cart of mass 20 kg, it moves with a uniform velocity on a horizontal floor. When a force of 1.2 P acts on the cart, it moves with an acceleration of 0.05 m/s2. Find the value of P.

12. Figure 3.E2 shows the velocity-time graph for a particle moving in a fixed direction, (a) Find the acceleration of the particle, (b) If the mass of the particle is 200 g, what is the force acting on it?

13. A force produces an acceleration of 1.5 m/s2 in a disk. Three such disks are tied together and the same force is applied on the combination. What will be the acceleration?

14. A constant force of 12 N acts on a body for 4 s. Find the change in the linear momentum of the body.

15. Two particles A and B of mass 10 g and 20 g respectively fall vertically. At a given time, the speed of particle A is 12 m/s and that of B is 15 m/s. Find the total linear momentum of the system of the two particles.

16. Two bodies A and B of mass 150 g and 250 g respectively are approaching each other. Both particles have a speed of 3 m/s. Find the magnitude of the total linear momentum of the system of the two particles.

17. A boy weighing 30 kg is riding a bicycle weighing 50 kg. If the bicycle is moving at a speed of 9 km/h towards the west, find the linear momentum of the bicycle-boy system in SI units.

18. A block of mass 120 g moves with a speed of 6.0 m/s on a frictionless horizontal surface towards another block of mass 180 g kept at rest. They collide and the first block stops. Find the speed of the other block after the collision.

19. A ball of mass 100 g and another ball of 120 g moves towards each other with speeds 6 m/s and 5 m/s respectively. If they stick to each other after colliding, What would be the velocity of the combined mass after the collision?

20. A cart of mass 50 kg is moving on a straight track with a speed of 12 m/s. A mass of 10 kg is gently put into the cart. What will be the velocity of the cart after this?

21. A force of 12 N is uniformly distributed over an area of 120 cm 2. Find the pressure in pascals.

22. How much force should be applied on an area of • 1 cm 2 to get a pressure of 12 Pa?

23. A block weighing 1.0 kg is in the shape of a cube of length 10 cm. It is kept on a horizontal table. Find the pressure on the portion of the table where the block is kept.

24. A body of volume 50 cm3 is completely immersed in water. Find the force of buoyancy on it.

25. A metallic sphere of radius 2.00 cm is completely immersed in water. Find the force of buoyancy on it.

26. A body of mass 2.0 kg and density 8,000 kg/m3 is completely immersed in a liquid of density 800 kg/m3. Find the force of buoyancy on it.

27. A body of mass 2.0 kg floats in a liquid. What is the buoyant force on the body?

1.1.47 N upwards

2. (a) 4 N upwards (b) 4 N downwards

(c) 4 N downwards (d) 4 N upwards

3.0.04 N 4.25 m/s2 5.2 s 6.0,30 N

7. (a) 8 m/s (b) 64 m

8. 0.001 N

9.2.5 N, earth 10. zero

11.5 N 12. (a) 4 m/s2 (b) 0.8 N

13.0.5 m/s2 14.48 kg m/s

15.0.42 kg m/s downwards 16.0.30 kg m/s

17. 200 kg m/s 18.4 m/s 19.0 20.10 m/s

21.1,000 Pa 22.1.2 x 10"3 N 23.980 Pa

24.0.49 N 25.0.328 N 26.1.96 N

27.19.6 N