# Engineering Physics Questions and Answers – Acceleration

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This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Acceleration”.

1. A gun fires a bullet of mass 50g with a velocity of 30m/s. Because of this, the gun is pushed back with a velocity of 1m/s. The mass of the gun is?
a) 5.5kg
b) 3.5lg
c) 1.5kg
d) 0.5kg

Explanation: By conservation of momentum, MV = mv
M = mv/V = (0.05×30)/1 = 1.5kg.

2. Rocket engines lift a rocket from the earth surface because of hot gases with high velocity ___________
a) Push against the air
b) Push against the earth
c) React against the rocket and push it up
d) Heat up the air which lifts the rocket

Explanation: Rocket engines live a rocket from the earth surface because hot gases with high velocity react against the rocket and push it up. Hot gases with high velocity react against the rocket and push it up.

3. The motion of a rocket is based on the principle of conservation of ___________
a) Linear momentum
b) Angular momentum
c) Kinetic energy
d) Mass

Explanation: A rocket works on the principle of conservation of linear momentum.
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4. A bullet is fired from the rifle. If the rifle recoils freely, then the kinetic energy of the rifle is ___________
a) Less than the kinetic energy of the bullet
b) More than the kinetic energy of the bullet
c) Same as the kinetic energy of the bullet
d) Equal or less than the kinetic energy of the bullet

Explanation: By conservation of momentum,
MV = mv or V = mv/M
Kinetic energy of the rifle is
Kr = 1/2MV2 = 1/2M(m2 v2)/M2
Kr = m/M * Kb
As m is lesser than M, Kr is lesser than Kb
Thus the kinetic energy is less than that of the bullet.

5. A person is standing in an elevator. In which situation he finds his weightless?
a) When the elevator moves upward with constant acceleration
b) When the elevator moves downward with constant acceleration
c) When the elevator moves upward with uniform velocity
d) When the elevator moves downward, with uniform velocity

Explanation: When the elevator moves downward with acceleration a, the apparent weight, W=m(g-a) is lesser than W(=mg).

6. A person with a spring balance with a body hanging from it goes up in an aeroplane, then the reading of the weight of the body as indicated by the spring balance will ___________
a) Go on increasing
b) Go on decreasing
c) First increases and then decreases
d) Remains the same

Explanation: As the person goes above the earth’s surface, the value of g decrease. Hence the reading in the spring balance will go on decreasing.

7. Assertion: On a rainy day, it is difficult to drive at high speed.
Reason: The value of the coefficient of friction is lowered due to wetting of the surface.
a) If both assertion and reason are true and the reason is the correct explanation of the assertion
b) If both assertion and reason are true but the reason is not correct explanation of the assertion
c) If assertion is true, but the reason is false
d) If both assertion and reason are false

Explanation: Both assertion and reason are true. Due to wetting, friction decreases between tyres and road. This may lead to skidding of the vehicle.

8. A monkey of mass 20 kg is holding a vertical rope. The rope will not break when a mass of 25 kg is suspended from it but will break if the mass exceeds 25kg. What is the minimum acceleration with which the monkey can climb up along the rope? (g = 10m/s2)
a) 5m/s2
b) 10m/s2
c) 25m/s2
d) 2.5m/s2

Explanation: When the monkey climbs up the rope with acceleration a,
T = m(g+a)
Mg = mg+ma
25×10=20×10+20a
a = 2.5m/s2.

9. A block has been placed on an inclined plane with the slope angle θ, block slides down the plant at a constant speed. The coefficient of kinetic energy is equal to ____________
a) sinθ
b) cosθ
c) g
d) tanθ

Explanation: As the block slides down the inclined plane with a constant speed, the angle of inclination is equal to the angle of response.
μ = tangent of the angle of response
μ = tanθ.

10. A man is standing on a spring platform. Reading of spring balance is 60kg wt. If the man jumps outside from the platform, then the reading of spring balance will ___________
a) Increase
b) Become zero
c) Remains same
d) First increases and then becomes zero

Explanation: To jump outside the platform, the man pushes the platform, so the reading of the spring balance first increases and then becomes zero.

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