1. A 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: When a force F acts on an object to move it in its direction through a distance S, work is done.
The work on the body is done by force.
Work done = Force × Displacement
W = F × S
Where,
F = 7 N S = 8 m
So, work done,
W = 7 × 8
W = 56 Nm
W = 56 J
2. When do we say that work is done?
Ans: Work is said to be done when the following conditions are satisfied:
(i) A force acts on the body.
(ii) The body undergoes a displacement due to the applied force, and the displacement occurs in the direction of the force (or opposite to it).
If both conditions are met, work is done on the object.
3. Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Ans: When a force F acts on an object and displaces it through a distance SS in the direction of the applied force, the work done W on the body is given by the expression:
W=F×S
where:
F is the applied force,
S is the displacement of the object.
W=F×S
where:
F is the applied force,
S is the displacement of the object.
4. Define 1 J of work.
Ans:
1 J is the amount of work done on an object when a force of 1 N displaces it by 1 m along the line of action of the force.
5. A 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 by the bullocks is given by the expression:
W= F × d
Where,
Applied force, F = 140 N
Displacement, d = 15 m
W = 140 x 15 = 2100 J
Therefore, 2100 J of work is done in ploughing the length of the field.
How much work is done in ploughing the length of the field?
Ans:
Work done by the bullocks is given by the expression:
W= F × d
Where,
Applied force, F = 140 N
Displacement, d = 15 m
W = 140 x 15 = 2100 J
Therefore, 2100 J of work is done in ploughing the length of the field.
6. What is the kinetic energy of an object?
Ans: Kinetic energy is the energy possessed by an object due to its motion. Every moving object has kinetic energy, which is a form of mechanical energy. The energy is used by the object to perform work. For example, the kinetic energy of a hammer is used to drive a nail into a log of wood, and the mechanical energy of moving air is used to run windmills. The kinetic energy depends on the mass and velocity of the object.