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#### Laws of Motion - Important Question Paper

11th Standard

Reg.No. :
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Physics

Time : 01:00:00 Hrs
Total Marks : 50

Part A

10 x 1 = 10
1. A vehicle is moving along the positive x direction, if sudden brake is applied, then

(a)

frictional force acting on the vehicle is along negative x direction

(b)

frictional force acting on the vehicle is along positive x direction

(c)

no frictional force acts on the vehicle

(d)

frictional force acts in downward direction

2. Two blocks of masses m and 2m are placed on a smooth horizontal surface as shown. In the first case only a force F1 is applied from the left. Later only a force F2 is applied from the right. If the force acting at the interface of the two blocks in the two cases is same, then F1 :F2 is

(a)

1:1

(b)

1:2

(c)

2:1

(d)

1:3

3. Force acting on the particle moving with constant speed is

(a)

always zero

(b)

need not be zero

(c)

always non zero

(d)

cannot be concluded

4. When an object is at rest on "the inclined rough surface

(a)

static and kinetic frictions acting on the object is zero

(b)

static friction is zero but kinetic friction is not zero

(c)

static friction is not zero and kinetic friction is zero

(d)

static and kinetic frictions are not zero

5. The centrifugal force appears to exist

(a)

only in inertial frames

(b)

only in rotating frames

(c)

in any accelerated frame

(d)

both in inertial and non-inertial frames

6. Three blocks of masses m1, m2 and m3 are placed on a horizontal frictionless surface. A force of 40 N pulls the system , then calculate the value of T, if m1 = 10 kg, m2 = 6kg, m3 = 4 kg.

(a)

40 N

(b)

20 N

(c)

10 N

(d)

5 N

7. Three identical blocks of masses m - 2 kg are drawn by a force F = 10.2 N with an acceleration of 0.6 ms-2 on a frictionless surface, then what is the tension  (in N) in the string between the blocks B and C?

(a)

9.2 N

(b)

7.8 N

(c)

4 N

(d)

9.8 N

8. A rope of length L and mass M is hanging from a rigid support. The tension in the rope at a distance x from the rigid support is

(a)

Mg

(b)

$\left( \frac { L-x }{ L } \right) Mg$

(c)

$\left( \frac { L }{ L-x } \right) Mg$

(d)

$\frac { x }{ L } Mg$

9. A weightless rod is acted upon by upward parallel forces of 4 N and 2 N magnitudes at ends A and B respectively. The total length of the rod AB = 3 m. To keep the rod in equilibrium a force of 6 N should act in the following manner

(a)

downward at any point between A and B

(b)

downward at the midpoint of AB

(c)

downward at a point C such that AC = 1 m

(d)

downward at a point C such that BC = 1 m

10. A truck weighing 1000 kg is moving with velocity of 50 km/h on smooth horizontal roads. A mass of 250 kg is dropped into it. The velocity with which it moves now is

(a)

12.5 km/h

(b)

20 km/h

(c)

40 km/h

(d)

50 km/h

11. Part B

6 x 2 = 12
12. Give reason "If the object is pressed hard on the surface where it is placed. As a result it is more difficult to move the object".

13. Does the force of friction depends on the area of contact?

14. It is easier to roll a barrel than to pull it along the road. Why?

15. Give reason. fs = μs.N

16. Define coefficient of static friction.

17. What is the need of banking a circular road?

18. Part C

6 x 3 = 18
19. When a person walks on a surface, the frictional force exerted by the surface on the person is opposite to the direction of motion. True or false?

20. Can the coefficient of friction be more than one?

21. Can we predict the direction of motion of a body from the direction of force on it?

22. The momentum of a system of particles is always conserved. True or false?

23. What are the steps which have to be followed before applying Newton's laws?

24. The Two masses m1=m2 =0.5kg are connected by a string which passes over a smooth frictionless pulley. What is the,acceleration of the masses

25. Part D

2 x 5 = 10
26. Prove the law of conservation of linear momentum. Use it to find the recoil velocity of a gun when a bullet is fired from it.

27. Explain the motion of blocks connected by a string in Horizontal motion.