DELHI PUBLIC SCHOOL, KNOWLEDGE PARK V
CLASS: XI
SUBJECT: PHYSICS
WORKSHEET: CHAPTER 4 – FORCE
Q1. The tension in the string shown in figure is:
(a) F/3 (b) F/6 (c) F/2 (d) 2F
Q2. A particle moves in x-y plane under the action of force 𝐹⃗ such that the value of its linear
momentum (𝑃⃗⃗) at any instant t is Px = 2cos(t) and Py = 2sin(t). The angle 𝜃 between 𝐹⃗ and 𝑃⃗⃗
at a given time t will be-
(a) 900 (b)1800 (c) 00 (d)300
Q3. Three forces 𝐴⃗ = 𝑖̂ + 𝑗̂ − 𝑘̂ , 𝐵
⃗⃗ = 2𝑖̂ − 𝑗̂ + 3𝑘̂ and 𝐶⃗ are acting on a body to keep it in
equilibrium. Then C is
(a) 3𝑖̂ + 4𝑘̂ (b)−3𝑖̂ − 2𝑘̂ (c) )−3𝑖̂ + 2𝑘̂ (d)−3𝑖̂ + 4𝑘̂
Q4. The objects at rest suddenly explodes into three parts with the mass ratio 2: l: l. The parts of
equal masses move at right angles to each other with equal speeds (v). The speed of the third
part after the explosion will be
(a) 2v (b) v/√2 (c) v/2 (d) √2v
Q5. Three block of masses m1, m2 and m3 are connected by mass less stings as shown on a
frictionless table.
They are pulled with a force T3 = 40N. If m1 = 10kg, m2 = 6kg and m3 = 4kg, then tension T2
will be:
(a) 20N (b) 40N (c) 10N (d) 32N
Q6. If the tension in the cable supporting an elevator is equal to the weight of elevator, the
elevator may be
(a) going up with increasing speed
(b) going down with increasing speed
(c) going up with uniform speed
(d) elevator falls freely under gravity
Q7. A graph is drawn with a force along y-axis and time along x-axis. The area under the graph
represent—
(a) Momentum (b) Moment of the force
(c) Couple (d) Impulse of the force
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Q8. A bullet of mass m moving with a speed v strikes a wooden block of mass M & gets
embedded into the block. The final speed is
Q9. The pulley & strings shown in figure are smooth and of negligible mass. For the system to
remain in equilibrium, the angle 𝜃 should be
(a) 600 (b) 450 (c) 00 (d)300
Q10. In the figure given, the position-time graph of a particle of mass 0.1 kg is shown, the impulse
at t = 2s is
(a) 0.2 kg m/s (b) - 0.2 kg m/s (c) 0.1 kg m/s (d) - 0.4 kg m/s
Q11. If mass of body is increased by 10% and its speed is decreased by 10% then the percentage
change in magnitude of momentum will be
(a) Increased by 1% (b) Decreased by 1% (c) Increased by 2% (d) Decreased by 2%
Q12. A body with mass 5 kg is acted upon by a force 𝐹⃗ = (−3𝑖̂ + 4𝑗̂)N. If its initial velocity at t =
0 is 𝑢
⃗⃗ = 6𝑖̂ − 12𝑗̂ m/s, the time at which it will just have a velocity along the Y-axis is:
(a) never (b) 2 s (c) 10 s (d) 15 s
Q13. A player catches a ball of 100 g moving with a speed of 5 m/s. If the time taken to complete
the catch is 0.25 s, the force exerted on the player's hand is: -
(a) 8 N (b) 4 N (c) 2 N (d) 0 N
Q14. n bullet strike per second elastically on a wall with speed V and rebound. what will be the
force exerted on the wall by bullets if mass of each bullet is m: -
(a) mnv (b) 4mnv (c) 2mnv (d) mnv/2
Q15. A body of mass 2 kg has an initial speed 5 ms -1. A force acts on it for some time in the
direction of motion. The force-time graph is shown in figure. The final speed of the body is: -
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(a) 9.25 ms-1 (b) 5 ms-1 (c) 14.3 ms-1 (d) 4.25 ms-1
Q16. A body of mass M at rest explodes into three pieces, two of which of mass M/4 each are
thrown off in perpendicular directions with velocities of 3 m/s and 4 m/s respectively. The
third piece will be thrown off with a velocity of
(a) 1.5 m/s (b) 2.5 m/s (c) 2.0 m/s (d) 3.0 m/s
Q17. The figure shows a horizontal force 𝐹⃗ acting on a block of mass M on an inclined plane
(angle 𝜃). What is the normal reaction on the block?
(a) mgsin𝜃 + Fcos𝜃 (b) mgsin𝜃 −Fcos𝜃
(c) mgcos𝜃 –Fsin𝜃 (d) mgcos𝜃 + Fsin𝜃
Q18. A uniform sphere of weight W and radius 3 m is being held by a string of length 5m attached
to a frictionless wall as shown in the figure. The tension in the string will be: -
(a) 5W/4 (b) 15W/4 (c) 15W/16 (d) None of these
Q19. A block of weight 40 N is supported by two ropes. One rope is horizontal and the other
makes an angle of 30° with the ceiling. The tension in the rope attached to the ceiling is
approximately.
(a) 80 N (b) 40 N (c) 20 N (d) 10 N
Q20. In the fig. mass m = 10 kg then in order to keep it at rest, the value of mass M will be: -
(a) 10 kg (b) 5 kg (c) 20 kg (d) 40 kg
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Q21. Assertion (A) : A rocket moves forward by pushing the surrounding air backwards.
Reason (R) : It drives the necessary thrust to move forward according to Newton's third law
of motion.
Q22. Assertion (A) : A table cloth can pulled from a table without disloding the dishes.
Reason (R) : To every action there is an equal and opposite reaction.
Q23. Three masses of 1 kg, 6 kg and 3 kg are connected to each other with threads and are placed
on a table as shown in figure. Find the ratio T1/T2 is: - (Take g = 10 m/s2)
Q24. Two blocks of mass 3M and 4M are resting on frictionless inclined planes as shown in fig.
Find acceleration of the system.
Q25. Two bodies of masses 15 kg and 5 kg are arranged in two different ways as shown in fig. (A)
and (B). if the pulleys and the table are perfectly smooth, find the acceleration of the 5 kg
body in case (A) and (B).
Q26. What will be the acceleration of the blocks if they are set free to move? (g = acceleration due
to gravity)
Q27. There are few forces acting at a Point P produced by strings as shown, which is at rest, Find
the forces F1 & F2
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Q28. Fig shows a light rope fixed at one end to a clamp on the ground and its other end passing
over the branch of a tree and hanging on the other side of it. The rope makes an angle of 30o
with the ground. A boy weighing 45kg starts climbing up the rope. Find the maximum
acceleration with which the boy can climb safely, if the clamp comes out of ground, when a
force of 270N acts on it vertically upwards. Assume that there is no friction between the rope
and the tree branches.
Q29. Two blocks of mass 2 kg and 5 kg are connected by an ideal string passing over a pulley. The
block of mass 2 kg is free to slide on a surface inclined at an angle of 300 with the horizontal
whereas 5 kg block hangs freely. Find the acceleration of the system and the tension in the
string.
Q30. In terms of m1; m2 and g find the acceleration of both the blocks as shown.
ANSWERS: Q1 (a) Q2 (a) Q3 (b) Q4 (b) Q5 (d) Q6 (c) Q7 (d) Q8 (c) Q9 (b) Q10 (b) Q11 (b) Q12
(c) Q13 (c) Q14 (c) Q15 (c) Q16 (b) Q17 (d) Q18 (a) Q19 (a) Q20 (c) Q21 (a) Q22 (b)
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