Laws of Motion Questions and Answers Part-3

1. A body of mass 40 gm is moving with a constant velocity of 2 cm/sec on a horizontal frictionless table. The force on the table is
a) 39200 dyne
b) 160 dyne
c) 80 dyne
d) Zero dyne

Answer: a
Explanation: Force on the table = mg = 40 * 980 = 39200 dyne

2. When 1 N force acts on 1 kg body that is able to move freely, the body receives
a) A speed of 1 m/sec
b) An acceleration of \[1 m\diagup sec^{2}\]
c) An acceleration of \[980 cm\diagup sec^{2}\]
d) An acceleration of \[1 cm\diagup sec^{2}\]

Answer: b

3. An object with a mass 10 kg moves at a constant velocity of 10 m/sec. A constant force then acts for 4 second on the object and gives it a speed of 2 m/sec in opposite direction. The acceleration produced in it, is
a) 3 \[m\diagup sec^{2}\]
b) -3 \[m\diagup sec^{2}\]
c) 0.3 \[m\diagup sec^{2}\]
d) -0.3 \[m\diagup sec^{2}\]

Answer: b

4. In the above question, the force acting on the object
a) 30 N
b) – 30 N
c) 3 N
d) – 3 N

Answer: b
Explanation: F = ma = 10 * (−3) = −30 N

5. In the above question, the impulse acting on the object is
a) 120 Newton \[\times\] sec
b) -120 Newton \[\times\] sec
c) 30 Newton \[\times\] sec
d) -30 Newton \[\times\] sec

Answer: b
Explanation: Impulse = Force * Time = −30 * 4 = −120 N-s

6. A machine gun is mounted on a 2000 kg car on a horizontal frictionless surface. At some instant the gun fires bullets of mass 10 gm with a velocity of 500 m/sec with respect to the car. The number of bullets fired per second is ten. The average thrust on the system is
a) 550 N
b) 50 N
c) 250 N
d) 250 dyne

Answer: b

7. In the above question, the acceleration of the car will be
a) 0.25 \[m\diagup sec^{2}\]
b) 25 \[m\diagup sec^{2}\]
c) 5.0 \[m\diagup sec^{2}\]
d) 0.025 \[m\diagup sec^{2}\]

Answer: d

8. A particle of mass 0.3 kg is subjected to a force \[k=-kx\] with \[k=15N\diagup m\] . What will be its initial acceleration if it is released from a point 20 cm away from the origin
a) 5 \[m\diagup sec^{2}\]
b) 10 \[m \diagup sec^{2}\]
c) 3 \[m\diagup sec^{2}\]
d) 15 \[m\diagup sec^{2}\]

Answer: b

9. A block of metal weighing 2 kg is resting on a frictionless plane. It is struck by a jet releasing water at a rate of 1 kg/sec and at a speed of 5 m/sec. The initial acceleration of the block will be
a) \[2.5m\diagup sec^{2}\]
b) \[5.0m\diagup sec^{2}\]
c) \[10m\diagup sec^{2}\]
d) None of the above

Answer: a

10. Gravels are dropped on a conveyor belt at the rate of 0.5 kg/sec. The extra force required in newtons to keep the belt moving at 2 m/sec is
a) 1
b) 2
c) 4
d) 0.5

Answer: a