Q3 of 26 Page 28

Rewrite the following sentences using proper alternative.

The potential energy of your body is least when you are …..


i. sitting on a chair


ii. sitting on the ground


iii. sleeping on the ground


iv. standing on the ground

Option(iii) sleeping on the ground

Explanation: Potential energy of any object depends upon its height from the surface of earth, We know the Relation for Potential energy of an object of mass m due to earth’s gravity(g is acceleration due to gravity) held at an height h above ground is


P.E. = mgh


So more is the height of body from ground more is the potential energy and less is the height of body from ground less is the potential energy


Now in case of human body height of body from ground is measured from center of mass of the body which is the point where all mass of the body is assumed to be concentrated , the position of which is near the stomach in human body , so potential energy of body will be least in case of a person sleeping because in that situation height of centre of mass of the body will be minimum from ground.


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2

Choose one or more correct alternatives.

Power is a measure of the ...….


i. the rapidity with which work is done


ii. amount of energy required to perform the work


iii. The slowness with which work is performed


iv. length of time

 2

Choose one or more correct alternatives.

While dragging or lifting an object, negative work is done by


i. the applied force


ii. gravitational force


iii. frictional force


iv. reaction force

 3

Rewrite the following sentences using proper alternative.

The total energy of an object falling freely towards the ground …


i. decreases


ii. remains unchanged


iii. increases


iv. increases in the beginning and then decreases

 3

Rewrite the following sentences using proper alternative.

If we increase the velocity of a car moving on a flat surface to four times its original speed, its potential energy….


i. will be twice its original energy


ii. will not change


iii. will be 4 times its original energy


iv. will be 16 times its original energy.