Define the term work. Name and define SI unit of work.
Give the sign of the work done by the force in the following case with
explanation. (i) Work done by gravitational force in lifting a bucket
out of a well by means of a rope tied to the bucket.
(ii) Work done by an applied force on a body moving on a rough
horizontal plane with uniform velocity
Answers
Explanation:
SI unit of work is joule
Answer:
(a) Positive
In the given case, force and displacement are in the same direction. Hence, the sign of work done is positive. In this case, the work is done on the bucket.
(b) Negative
In the given case, the direction of force (vertically downward) and displacement (vertically upward) are opposite to each other. Hence, the sign of work done is negative.
(c) Negative
Since the direction of frictional force is opposite to the direction of motion, the work done by frictional force is negative in this case.
(d) Positive
Here the body is moving on a rough horizontal plane. Frictional force opposes the motion of the body. Therefore, in order to maintain a uniform velocity, a uniform force must be applied to the body. Since the applied force acts in the direction of motion of the body, the work done is positive.
(e) Negative
The resistive force of air acts in the direction opposite to the direction of motion of the pendulum. Hence, the work done is negative in this case.