Science Question Answer (2 Marks)

Force, F = 2N
Distance, s = 10cm = 0.1m
Work done W = F × s
= 2 × 0.1 = 0.2J

Power of 1 fan = 120W
Power of 5 fans = 5 × 120
= 600 W = 0.6 kW
Time = 4 hours
Electrical energy = 0.6 × 4 = 2.4kWh

1. Kinetic energy: A moving cricket ball has kinetic energy.
2. Potential energy: A stretched rubber band has potential energy.

Work done is more when the boy pushes a bicycle because the force applied by him on the bicycle results in the motion of the bicycle. On the other hand, the boy trying to push a heavy truck parked on the roadside results in zero work, as there is no motion in the truck.

Yes, it is possible that a force is acting on a body but still work done is zero. For example, in the case of a man pushing a wall, the work done is zero despite of non-zero force, since there is no displacement of the wall.

1. Chemical energy to electrical energy.
2. Electrical energy to heat and light energy.

The work done by both X and Y are equal because irrespective of whether they reach the top of building by using a spiral or slanted ladder, the vertical distance moved by them against the gravity is same.

The work done against gravity is zero when a body is moved horizontally along a frictionless surface because force of gravity acts perpendicular to the direction of motion.

At a coal-based thermal power station, the chemical energy of coal is transformed into heat energy, which is further converted into kinetic energy and electrical energy.

Power = 100W

1. time = 1s

energy = power × time = 100 J

2. time = 1 minute = 60 s

energy = power × time

= 100 × 60 = 6kJ

1. Both kinetic and potential energy.
2. Both kinetic and potential energy.
3. Only kinetic energy.
4. Only potential energy.
5. Only potential energy.

Note: In all the above cases we take ground as reference level where potential energy is zero.

Gravitational potential energy of a body depends on:

1. Mass of the body, m.
2. Height to which the body is lifted, h.
3. Acceleration due to gravity, g.

A stretched rubber band is an example of a body possessing energy while it is not in motion. The rubber band contains potential energy due to the change in its shape or configuration.

Two examples where a body possesses both kinetic energy as well as potential energy are:

1. A man climbing up a hill.
2. A flying aeroplane.

The work done by a force on a body depends on two factors:

1. Magnitude of force.
2. Distance through which the body moves.

Work done is directly proportional to the force applied and the distance through which the body moves.
W = F × s
where W is work done, F is force applied and s is distance through which the body moves.

Work is done when a force applied on a body produces motion in it.
Formula for work done:
W = F × s
where W is the work done.
F is force applied.
S is the displacement of the body in the direction of force.

Yes, the kinetic energy of the ball thrown inside a moving bus depends on the speed of the bus because the speed of the bus adds up to the speed with which the ball is thrown inside the moving bus.

Mass = m
Height above the ground = h
Work done = Potential energy acquired by the body = m × g × h
where g is acceleration due to gravity.

1. Work done by force applied by the boy is positive because this force is in the direction of motion of the body.
2. Work done by the gravitational force is negative because this force is against the direction of motion of the body.

1. Maximum potential energy is present in the bob at point C as at point C bob is at maximum height.
2. Maximum kinetic energy is present in the bob at point A as at point A bob is at maximum speed.

1. Potential energy.
2. Both potential energy and kinetic energy.