Balbharati solutions for Science and Technology [English] 9 Standard Maharashtra State Board chapter 2 - Work and Energy [Latest edition]

Explain the difference between potential energy and kinetic energy. 

Derive the formula for the kinetic energy of an object of mass m, moving with velocity v.

Prove that the kinetic energy of a freely falling object on reaching the ground is nothing but the transformation of its initial potential energy.

Determine the amount of work done when an object is displaced at an angle of 30° with respect to the direction of the applied force.

If an object has 0 momentum, does it have kinetic energy? Explain your answer.

Why is the work done on an object moving with uniform circular motion zero?

Choose one or more correct alternatives.

For work to be performed, energy must be ______.

1. transferred from one place to another
2. concentrated
3. transformed from one type to another
4. destroyed

Choose one or more correct alternatives.

Joule is the unit of ______.

1. force
2. work
3. power
4. energy

Choose one or more correct alternatives.

Which of the forces involved in dragging a heavy object on a smooth, horizontal surface, have the same magnitude?

1. The horizontal applied force
2. gravitational force
3. reaction force in vertical direction
4. force of friction  

Choose one or more correct alternatives.

Power is a measure of the ______.

1. The rapidity with which work is done.
2. Amount of energy required to perform the work.
3. The slowness with which work is performed.
4. Length of time.

Choose one or more correct alternatives.

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

1. the applied force
2. gravitational force
3. frictional force
4. reaction force 

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

The total energy of an object falling freely towards the ground ______.

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

The work done on an object does not depend on ______.

1. Take two aluminium channels of different lengths.
2. Place the lower ends of the channels on the floor and hold their upper ends at the same height.
3. Now take two balls of the same size and weight and release them from the top end of the channels. They will roll down and cover the same distance.

An electric pump has 2 kW power. How much water will the pump lift every minute to a height of 10 m?

If a 1200 W electric iron is used daily for 30 minutes, how much total electricity is consumed in the month of April?

If the energy of a ball falling from a height of 10 metres is reduced by 40%, how high will it rebound?

The velocity of a car increases from 54 km/hr to 72 km/hr. How much is the work done if the mass of the car is 1500 kg?

Ravi applied a force of  10 N and moved a book 30 cm in the direction of the force. How much was the work done by Ravi?