set 2 MCQ Questions & Answers Detailed Explanation

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The following question based on mechanics (mass, force, acceleration, work, energy, momentum, velocity) topic of general science mcq

Questions : Rahul takes 1 minute to raise a box to a height of 1 metre and Rohan takes 1/2 minute to do so. Comment on the energy by the two.

(a) Energy spent by the Rohan is more

(b) Energy spent by both Rahul and Rohan is same.

(c) Energy spent by the Rahul is more.

(d) Cannot be said

The correct answers to the above question in:

Answer: (b)

Practice mechanics (mass, force, acceleration, work, energy, momentum, velocity) (set 2) Online Quiz

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Question : 1

A man getting down a running bus, falls forward because

a) he leans forward as a matter of habit

b) due to inertia of motion upper part of body continues to be in motion in forward direction while feet come to rest as soon as they touch the road

c) due to inertia of rest, road is left behind and man reaches forward

d) of the combined effect of all the three factors stated in (a), (b) and (c)

Answer: (b)

Question : 2

When a steady torque is acting on a body, the body

a) gets angular acceleration

b) gets linear acceleration

c) continues in its state of rest or uniform motion along a straight line

d) rotates at a constant speed

Answer: (a)

τ = Iα.

Here, α is the angular acceleration.

I is the rotational inertia, a property of a rotating system which depends on the mass distribution of the system.

The larger I, the harder it is for an object to acquire angular acceleration.

Question : 3

When a satellite is in the synchronous orbit above the equator, it stays in one place with reference to the earth by making each revolution in just the same time as it takes the earth to rotate once. What is the altitude of the synchronous orbit?

a) 32500 km

b) 30000 km

c) 20000 km

d) 36000 km

Answer: (d)

The period of revolution of the satellite must be exactly one day, or 86400s. The centripetal acceleration of the satellite must be $4π^2/T^2$ , the gravitational field must be

g = $g_0 (r_0/r)^2$. In free fall, a = g, so

$r=^3√{{(9.8m/{s}^2)(6.4×{10}^{-6}m)^2(86400s)^2}/{4π^2}}$

= 4.23 × $10^7$m

To get the altitude, subtract the radius of the earth. The satellite must be at an altitude of 36000 km.

Question : 4

The working principle of a washing machine is

a) Reverse osmosis

b) Dialysis

c) Centrifugation

d) Diffusion

Answer: (c)

Question : 5

Kepler’s second law (law of area) is nothing but a statement of

a) conservation of angular momentum

b) conservation of linear momentum

c) work energy theorem

d) conservation of energy

Answer: (a)

From Kepler's $2^{nd}$ law – The straight line joining the sun and the planet sweeps out equal areas in equal time intervals (${dA}/{dt}$ = const; area swept)

Areal velocity of the satellite is given by

${dA}/{dt}=1/2ωr^2 = const. = L/{2m}$

where ω = angular velocity of the satellite

L = mvr = mω$r^2$ = const, showing that Kepler's $2^nd$ law is a consequence of the conservation of angular momentum.

Question : 6

A gymnast takes turns with her arms & legs stretched. When she pulls her arms and legs

a) the angular velocity stays constant

b) the moment of inertia decreases

c) the angular velocity decreases

d) the angular momentum increases

Answer: (b)

GET mechanics (mass, force, acceleration, work, energy, momentum, velocity) PRACTICE TEST EXERCISES

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