# Engineering Physics Questions and Answers – Laws of Nature

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

1. A ship of mass 3×107kg initially at rest is pulled by a force of 5×104N through a distance of 3m. Assuming that the resistance due to water is negligible, the speed of the ship is?
a) 1.5m/s
b) 60m/s
c) 0.1m/s
d) 5m/s

Explanation: a = F/m = (5×104)/(3×107 )
Speed attained by the ship, v = √2as = 0.1m/s.

2. When a bicycle is in motion, the force of friction exerted by the ground on the two wheels is such that, it acts ___________
a) In the backward direction on the front wheel and in the backward direction on the rear wheel
b) In the forward direction on the front wheel and in the backward direction on the rear wheel
c) In the backward direction on both front and the back wheel
d) In the forward direction in both front and the back wheel

Explanation: When a bicycle is in motion, the force of friction acts in the backward direction on the front wheel and in the forward direction on the rear wheel.

3. A weight W rests on a rough horizontal plane. If the angle of friction is θ, the least force that will move the body along the plane will be ___________
a) W cosθ
b) W tanθ
c) W cotθ
d) W sinθ

Explanation: The least force required to move weight W on a horizontal plane is equal to the force of friction, f=μR=μmg or f= W tanθ.

4. Statement 1- A cloth covers a table. Some dishes are kept on it. The cloth can be pulled out without dislodging the dishes from the table.
Statement 2- For every action, there is an equal and opposite reaction.
a) Statement 2 is correct explanation for statement 1
b) Statement 2 is not correct explanation for statement 1
c) Statement 1 is true but statement 2 is false
d) Statement 1 is false but statement 2 is true

Explanation: The dishes will remain on the table due to the inertia of rest and not due to action-reaction forces. Statement 2 is not the correct explanation of statement 1.

5. A player caught a cricket ball of mass 150g moving at a rate of 20m/s. If the ball catching process is completed in 0.1s, the force on the blow exerted by the ball on the hand of the player is equal to ___________
a) 30N
b) 300N
c) 150N
d) 3N

Explanation: Impulse = change in momentum
F = (m(v-u))/t = -30N.

6. A machine gun fires a bullet of mass 40g with a velocity of 1200m/s =. The man holding it can exert a maximum force of 144N on the gun. How many bullets can he fire per second at the most?
a) One
b) Four
c) Two
d) Three

Explanation: Let the maximum number of bullets than can be fired per second be n
Change in momentum of n bullets = nm(v-u) = n×(40(1200-0))/1000 = 48n kgm/s
As impulse = Change in momentum
Ft = 48n
n = Ft/48 = 3bullets/second.

7. A light spring balance hangs from a hook of the other spring balance and a block of mass Mkg hangs from the former one. Then, which of the following is a true statement?
a) Both the scales read Mkg each
b) The scale of the lower one reads Mkg and of the upper one zero
c) The reading of the two scales can be anything but the sum of the readings will be Mkg
d) Both the scales read M/2 kg

Explanation: As the suspended spring balance is lighter one, both the scales will read Mkg each.

8. A particle is acted upon by a force of a constant magnitude which is always perpendicular to the velocity of the particle. The motion of the particle takes place in a plane. It follows that ___________
a) Its velocity is constant
b) Its acceleration is constant
c) Its kinetic energy is constant
d) It moves in a straight line

Explanation: It is a case of uniform motion in which velocity and acceleration vectors change due to change in direction. As the magnitude of velocity remains constant, the kinetic energy is constant.

9. A student unable to answer a question on Newton’s law of motion attempts to pull himself up by tugging on his hair. He will not succeed ___________
a) As the force exerted is small
b) The frictional force while gripping is small
c) Newton’s law of inertia is not applicable to living beings
d) As the force applied is internal to the system

Explanation: The force applied by the student into himself is an internal force. According to Newton’s law, only an external force can change the state of motion of an object.

10. A man of mass 60 kg and a boy of mass 30 kg are standing together on a frictionless ice surface. If they push each other apart, the man moves away with a speed of 0.4m/s relative to ice. After 5s they will be away from each other at a distance of ___________
a) 9 m
b) 3 m
c) 6 m
d) 30 m

Explanation: Momentum of man = -Momentum of boy
60×0.4 = -30×v
Velocity of the boy = -0.8m/s
Relative velocity = 0.4+0.8 = 1.2m/s
Distance between man and boy after 5s = 1.2×5 = 6 m.

Sanfoundry Global Education & Learning Series – Engineering Physics.

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