RADIANT CENTRAL CHILDREN ACADEMY
WORKSHEET- 1
CLASS- 9
SUBJECT - SCIENCE
1. When do we say that work is done?
2. Write an expression for the work done when a force is acting on an object in the
direction of its displacement.
3. Define 1 J of work.
4. A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15m
long. How much work is done in ploughing the length of the field?
5. A force of 10 N acts on an object. The object is displaced through 12 m, in the direction of
the force. If the force acts all through the displacement, find the work done by the force.
6. Calculate the work done by a student in lifting 0.5 kg book from the ground and keeping it on
a shelf 1.5m high.
7. A collie carries a load of 50 kg on his head and walks on a level road upto 100 m. What is the
work done by him?
8. A car weighing 1000 kg and traveling at 30m/s stops at a distance of 50m decelerating
uniformly. What is the force exerted on it by the brakes? What is the work done by the brakes?
9. When do we say that work is done?
10. Write an expression for the work done when a force is acting on an object in the
direction of its displacement.
11. Define 1 J of work.
12. What is power?
13. Define average power.
14. A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15m
long. How much work is done in ploughing the length of the field?
21. Two bodies of equal masses move with uniform velocities v and 3v respectively. Find the
ratio of their kinetic energies.
22. The mass of a ball A is double the mass of another ball B. The ball A moves at half the
speed of the ball B. Calculate the ratio of the kinetic energy of A to the kinetic energy of B.
23. A truck weighing 5000 kgf and a cart weighing 500 kgf are moving with the same speed.
Compare their kinetic energies.
24. A bullet of mass 20g is found to pass two points 30m apart in 4s? Assuming the speed to be
constant find its kinetic energy A 800g ball is pulled up a slope as shown in the diagram.
Calculate the potential energy it gains.
25. A spring is compressed by a toy cart of mass 150g. On releasing the cart, it moves with a speed
of 0.2m/s. Calculate the elastic potential energy of the spring.
26. An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential
energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
27. A box has a mass of 5.8kg. The box is lifted from the garage floor and placed on a shelf. If the
box gains 145 J of Potential Energy (Ep), how high is the shelf?
28. A man climbs on to a wall that is 3.6m high and gains 2268J of potential energy. What is the
mass of the man?
29. Below figure shows a ski- jump. A skier of mass
60 kg stands at A at the top of the ski- jump. He
moves from A to B and takes off his jump at B. (a)
Calculate the change in the gravitational potential
energy of the skier between A and B (b) If 75% of
the energy in part
(a) becomes the kinetic energy at B, calculate the
speed at which the skier arrives at B.
30. Consider the case of freely falling body given in
the figure:
At A,
Kinetic energy=0 and
Potential energy=mghAt
B,
Kinetic energy=mgxAt
C,
Kinetic energy=mgh and Potential energy=0
a) Find the potential energy of the body at B.
b) Find the total energy at A,B and C.
c) Is there any variation in total energy?
What do you infer from the result?
31. A bag of wheat weighs 200 kg. To what height should
it be raised so that its potential energy may be 9800
joules? (9.8 m/s2)
