Engineering Physics Multiple Choice Questions 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
Answer: c
Clarification: 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
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: b
Clarification: 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
Answer: a
Clarification: 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
Answer: d
Clarification: 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