State the sign of the work done in the following cases.
(a) work done by a person in lifting a bucket. (b) work done by the gravitational force in the above case.
Answers
Answer:
Both's answer is zero.
Ans.
(a) It is clear that the direction of both the force and the displacement are the same and thus the work done on it is positive.
(b) It can be noted that the displacement of the object is in an upward direction whereas, the force due to gravity is in a downward direction. Hence, the work done is negative.
(c) It can be observed that the direction of motion of the object is opposite to the direction of the frictional force. So, the work done is negative.
(d) The object which is moving in a rough horizontal plane faces the frictional force which is opposite to the direction of the motion. To maintain a uniform velocity, a uniform force is applied on the object. So, the motion of the object and the applied force are in the same direction. Thus, the work done is positive.
(e) It is noted that the direction of the bob and the resistive force of air which is acting on it are in opposite directions. Thus, the work done is negative.