CBSE-IX-Science
15: 1-Work and Energy
- #Science Work and Energy part 1
- #Section : I
- Qstn #1A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force. Let us take it that the force acts on the object through the displacement. What is the work done in this case?Ans : Since Work (W)
- #Section : II
- Qstn #1When do we say that work is done?Ans : Work is done when a force acts on an object and displacement occurs in the direction of force.
- Qstn #2Write an expression for the work done when a force is acting on an object in the direction of its displacement.Ans :
- Qstn #3Define 1 J of work.Ans : J is that work which is done when a force of 1N is applied on an object and it moves a distance of 1m in the direction of force.
- Qstn #4A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?Ans : Work done
- #Section : III
- Qstn #1What is the kinetic energy of an object?Ans : Kinetic energy of an object is a kind of mechanical energy and it is present in that object due to its state of motion(movement).
- Qstn #2Write an expression for the kinetic energy of an object.Ans : Kinetic energy =
where, m = mass of the object, v = velocity of the object(motion)
- Qstn #3The kinetic energy of an object of mass, m moving with a velocity of
is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?Ans : K.E. of the object =
= 2 kg
If velocity is doubled
= 200/2 = 100 J i.e. K.E. will become four times
If velocity is increased three times
= 225 J i.e. K.E. will become nine times
- #Section : IV
- Qstn #1What is power?Ans : Power is the rate of work done. It is denoted by P.
power = work/time
P = W / t
- Qstn #2Define 1 watt of power.Ans : If an agent works at the rate of 1 J/s then the power of that agent is 1 watt (where watt is the unit of power).