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QUESTION: 1

When a body falls freely under gravity, then the work done by the gravity is

Solution:

If a force acting on a body has a component in the direction of displacement, then the work done by the force is positive. Hence when a body falls freely under the influence of gravity the work done by the gravity is positive.

QUESTION: 2

There are two bodies X and Y with equal kinetic energy but different masses m and 4m respectively. The ratio of their linear momentum is-

Solution:

If X and Y have equal kinetic energy but their masses are m and 4m respectively. Thus we get the ratio of their speed is 2:1. Hence the ratio of their linear momentum is 1:2.

QUESTION: 3

Ram and sham together can complete a vocation in 8 days. Ram can do likewise work all alone in 12 days. To what extent will sham take to carry out the occupation without anyone else's input?

Solution:

(Ram + sham)'s 1 day work = 1 / 8,

Ram 1 day work = 1 / 12

Sham 1 day work = (1 / 8 - 1 / 12) = 1 / 24

∴ Sham alone can finish the work in 24 days.

QUESTION: 4

A truck moves at a steady speed on a horizontal road. What is the work done by the road on the truck?

Solution:

The work is zero because while the truck does have a displacement over time, the force of the road (the normal force) is perpendicular and so the dot product of the two is zero.

QUESTION: 5

Which of the following is not a unit of energy?

Solution:

Energy The joule ( symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metreor N⋅m).

QUESTION: 6

Which of the following statements is false:

Solution:

We know that KE = ½ mv^{2}

And as neither the mass nor v^{2} can be negative.

We get KE cant be negative.

QUESTION: 7

Raindrops fall on the earth with certain kinetic energy on the earth. From where do they get this energy?

Solution:

Every object that tends to fall or does fall on earth's surface does have a gravitational acceleration which is possessed by them due to their gravitational potential energy.

QUESTION: 8

Time rate at which work is done by a force is

Solution:

We know that Work done, W = F.s where F is force and s is displacement due to that force

Thus rate of work done = dW/dt = d(F.s)/dt

So as F is constant we get dW/dt = F.d(s)/dt

= F.v = P

QUESTION: 9

Output of a truck is 4500 J and its efficiency is 50%, the input energy provided to the truck is

Solution:

Changes(if required):

Solution:

η=50%= 50/100=1/2

So as we know, η=work output/heat input

1/2=4500/Heat input

Heat input =9000J

QUESTION: 10

When a body slides against a rough horizontal surface, the work done by friction is

Solution:

If a force acting on a body has a component in the opposite direction of displacement, the work done is negative, when a body slides against a rough horizontal surface, its displacement is opposite to that of the force of friction. He work done by the friction is negative.

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