KPK 11th Class Physics Chapter 4 Work and Energy Short Questions Answers

Yes, when a bucket is taken to the bottom of a well, some work is to be done against the up thrust of water. This work done is stored in the form of P.E in the bucket we can also say that the bucket posses some negative P.E with reference to the ground level.

To stretch the string of the bow, work is done on it. This work done is stored in the string as elastic P.E. on releasing the string of the bow, the stored elastic P.E is conuerted into the K.E of the arrow and makes it move m the forward direction. i.e.     (K.E)arrow= (P.E)bow  

Thus the arrow gets its K.E from the P.E of the bow.

Yes, A hydrogen filled balloon possess P.E. the hydrogen filled balloon is less denser than air, so when it is released in air. It moves in upwards direction against gravitational field due to up thrust of air. Thus work is done by the up thrust of air on the balloon which is stored in the form of P.E in the balloon.

We know that, K.E = 1/2mv² ………..(1)

In eq (1) ‘m’ represents the mass of a body which is a solar quantity. While ‘v²‘ represents the magnitude of velocity. As the magnitude represents a scalar quantity. So K.E is a scalar quantity. The K.E depends upon the magnitude of velocity. It does not depends upon the direction of velocity. Therefore K.E is a scalar quantity.

A target offers resistive force to a bullet, when it penetrates into it. The resistive force offered by the target does negative work on the bullet. So some of the K.E is used against the resistive force of the target material. Some parts of K.E may also be appear in the form of P.E and heat energy and also in the form of sound energy.

We know that, w = F.d ……………………….  (1)

Where ‘F’ is the applied force and ‘d’ is the displacement covered.

Since, in case of swinging pendulum, no displacement is covered along the string i,e in the direction of the tension in the string, so we put S=o in equation (1), so we get,   

W =f.o

• W=o

Therefore, the tension in the string of a swinging pendulum does no work, as there is no displacement covered in the direction of the tension in the string.

When a meteor enters into earths atmosphere, it burns due to friction b/w air particle and its body. Hence the energy possessed by a meteor is converted into heat and light energy due to which the energy of the particles of the medium [air] increases.

Elastic potential energy is stored in the spring of a watch, which is given by,

P.E   =  1/2kx²

When a man drops a cup from a certain height, its P.E is converted into K.E. When the cup strikes the ground, it breaks into pieces and its K.E is converted into heat and sound energy.

No work is by the man rowing boat upstream, if he is at rest with respect to the shore.

We know that, w = F.d _____ (1)

As no displacement d=o in equation (1) so we get, 

              W   =   f.o    => w=o

So no work is done by the man rowing a boat upstream, if he is at rest with respect to the shore.

Energy savers are used instead of normal bulb due to the following reasons

1. The consumption of energy in energy savers is far less than normal light bulbs.
2. Energy savers produces light of high power and intensity as compared to normal light bulbs.
3. Energy savers are of long livers as compared to normal light bulbs.
4. Energy savers are more safer than ordinary light bulbs, as they produce very little amount of heat.