JEE Physics Laws Of Motion MCQs Set A

Question. An athlete does not come to rest immediately after crossing the winning line due to the
(a) Inertia of motion
(b) Inertia of rest
(c) Inertia of direction
(d) None of these

Answer: A

Question. When an object is at rest
(a) A large number of forces may be acting on it which balance each other
(b) It is in vacuum
(c) No force is acting on it
(d) Force is required to keep it in rest state

Answer: A

Question. Newton’s first law is applicable
(a) Only in inertial reference frames
(b) In all reference frames
(c) Only in non-inertial reference frames
(d) None of these

Answer: A

Question. From Newton’s second law of motion, it can be inferred that
(a) All of these
(b) No force is required to move a body uniformly along straight line
(c) Accelerated motion is always due to an external force
(d) Inertial mass of a body is equal to force required per unit acceleration in the body

Answer: A

Question. If a force of constant magnitude acts in direction perpendicular to the motion of a particle, then its
(a) Speed is uniform
(b) Momentum is uniform
(c) Velocity is uniform
(d) All of these

Answer: A

Question. When an object is in equilibrium state, then
(a) Its net acceleration must be zero
(b) It must be at rest
(c) No force is acting on it
(d) All of these

Answer: A

Question. When a force of constant magnitude and a fixed direction acts on a moving object, then its path is
(a) Either (2) or (3)
(b) Straight line
(c) Parabolic
(d) None of these

Answer: A

Question. A body of mass 2 kg is sliding with a constant velocity of 4 m/s on a frictionless horizontal table. The force required to keep the body moving with the same velocity is
(a) 0 N
(b) 2 × 10⁴ N
(c) 8 N
(d) None of these

Answer: A

Question. A 10 g bullet moving at 200 m/s stops after penetrating 5 cm of wooden plank. The average force exerted on the bullet will be
(a) –4000 N
(b) 4000 N
(c) –2000 N
(d) 2000 N

Answer: B

Question. A ball of mass 50 g is dropped from a height of 20 m. A boy on the ground hits the ball vertically upwardsb with a bat with an average force of 200 N, so that it attains a vertical height of 45 m. The time for which the ball remains in contact with the bat is [Take g = 10 m/s²]
(a) 1/80th of a second
(b) 1/120th of a second
(c) 1/40th of a second
(d) 1/20th of a second

Answer: A

Question. A string tied on a roof can bear a maximum tension of 50 kg wt. The minimum acceleration that can be acquired by a man of 98 kg to descend will be [Take g = 9.8 m/s²]
(a) 4.8 m/s²
(b) 5 m/s²
(c) 4.9 m/s²
(d) 9.8 m/s²

Answer: A

Question. In accordance with Newton’s third law of motion
(a) All of these
(b) This law is applicable whether the bodies are at rest or they are in motion
(c) For appearance of action and reaction, physical contact is not necessary
(d) Action and reaction never balance each other

Answer: A

Question. A man of mass 50 kg carries a bag of weight 40 N on his shoulder. The force with which the floor pushes up his feet will be
(a) 530 N
(b) 882 N
(c) 90 N
(d) 600 N

Answer: A

Question. In a rocket, fuel burns at the rate of 2 kg/s. This fuel gets ejected from the rocket with a velocity of 80 km/s. Force exerted on the rocket is
(a) 1,60,000 N
(b) 1600 N
(c) 16 N
(d) 16,000 N

Answer: A

Question. A machine gun fires a bullet of mass 65 g with a velocity of 1300 m/s. The man holding it can exert a maximum force of 169 N on the gun. The number of bullets he can fire per second will be
(a) 2
(b) 1
(c) 3
(d) 4

Answer: A

Question. A bullet of mass 40 g is fired from a gun of mass 10 kg. If velocity of bullet is 400 m/s, then the recoil velocity of the gun will be
(a) 1.6 m/s opposite to the direction of bullet
(b) 1.8 m/s opposite to the direction of bullet
(c) 1.6 m/s in the direction of bullet
(d) 1.8 m/s in the direction of bullet

Answer: A

Question. A cracker rocket is ejecting gases at a rate of 0.05 kg/s with a velocity 400 m/s. The accelerating force on the rocket is
(a) 20 N
(b) 20 dyne
(c) 200 N
(d) Zero

Answer: A

Question. A rocket of mass 5700 kg ejects mass at a constant rate of 15 kg/s with constant speed of 12 km/s. The acceleration of the rocket 1 minute after the blast is (g = 10 m/s²)
(a) 27.5 m/s²
(b) 34.9 m/s²
(c) 3.50 m/s²
(d) 13.5 m/s²

Answer: A

Question. A balloon has 2 g of air. A small hole is pierced into it. The air comes out with a velocity of 4 m/s. If the balloon shrinks completely in 2.5 s. The average force acting on the balloon is
(a) 0.0032 N
(b) 0.008 N
(c) 8 N
(d) 3.2 N

Answer: A

Question. A 6 kg bomb at rest explodes into three equal pieces P, Q and R. If P flies with speed 30 m/s and Q withspeed 40 m/s making an angle 90° with the direction of P. The angle between the direction of motion of P and R is about
(a) 127°
(b) 120°
(c) 150°
(d) 143°

Answer: A

Question. A particle of mass 2m moving with velocity v strikes a stationary particle of mass 3m and sticks to it. The speed of the system will be
(a) 0.4v
(b) 0.6v
(c) 0.2v
(d) 0.8v

Answer: A

Question. Which of the following is self-adjusting force?
(a) Static friction
(b) Limiting friction
(c) Kinetic friction
(d) Rolling friction

Answer: A

Question. Maximum force of friction is called
(a) Limiting friction
(b) Static friction
(c) Sliding friction
(d) Rolling friction

Answer: A

Question. The limiting friction between two bodies in contact is independent of
(a) The area of surfaces in contact
(b) The materials of the bodies
(c) Nature of the surface in contact
(d) Normal reaction between the surfaces

Answer: A

Question. It is difficult to move a cycle with brakes on because
(a) Sliding friction is more than the rolling friction
(b) Sliding friction opposes motion on road
(c) Rolling friction opposes motion on road
(d) Rolling friction is more than sliding friction

Answer: A

Question. Which is a suitable method to decrease friction?
(a) All of these
(b) Ball bearing
(c) Lubrication
(d) Polishing

Answer: A

Question. A child weighing 25 kg slides down a rope hanging from a branch of a tall tree. If the force of friction acting against him is 200 N, the acceleration of child is (g = 10 m/s²)
(a) 2 m/s²
(b) 5 m/s²
(c) 8 m/s²
(d) 22.5 m/s²

Answer: A

Question. An object of mass 1 kg moving on a horizontal surface with initial velocity 8 m/s comes to rest after 10s. If one wants to keep the object moving on the same surface with velocity 8 m/s the force required is
(a) 0.8 N
(b) 1.2 N
(c) Zero
(d) 0.4 N

Answer: A

Question. A heavy box is solid across a rough floor with an initial speed of 4 m/s. It stops moving after 8 seconds. If the average resisting force of friction is 10 N, the mass of the box (in kg) is
(a) 20
(b) 40
(c) 5
(d) 2.5

Answer: A

Question. If a block moving up an inclined plane at 30° with a velocity of 5 m/s, stops after 0.5 s, then coefficient of friction will be nearly
(a) 0.6
(b) 0.5
(c) 0.9
(d) 1.1

Answer: A

Question. Two blocks A and B of masses 5 kg and 3 kg respectively rest on a smooth horizontal surface with B overA. The coefficient of friction between A and B is 0.5. The maximum horizontal force (in kg wt.) that can be applied to A, so that there will be motion of A and B without relative slipping, is
(a) 4
(b) 5
(c) 2.5
(d) 1.5

Answer: A

Question. A bus turns a slippery road having coefficient of friction of 0.5 with a speed of 10 m/s. The minimum radius of the arc in which bus turns is [Take g = 10 m/s²]
(a) 20 m
(b) 15 m
(c) 10 m
(d) 4 m

Answer: A