Identify the correct statements from the following:
(A) Work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket is negative.
(B) Work done by gravitational force in lifting a bucket out of a well by a rope tied to the bucket is negative.
(C) Work done by friction on a body sliding down an inclined plane is positive.
(D) Work done by an applied force on a body moving on a rough horizontal plane with uniform velocity in zero.
(E) Work done by the air resistance on an oscillating pendulum in negative.
Choose the correct answer from the options given below:
(A) Work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket is negative.
(B) Work done by gravitational force in lifting a bucket out of a well by a rope tied to the bucket is negative.
(C) Work done by friction on a body sliding down an inclined plane is positive.
(D) Work done by an applied force on a body moving on a rough horizontal plane with uniform velocity in zero.
(E) Work done by the air resistance on an oscillating pendulum in negative.
Choose the correct answer from the options given below:
- (A)B and E only✓ Correct
- (B)A and C only
- (C)B, D and E only
- (D)B and D only
Answer: (A)
Solution
Lifting the bucket, the man pulls up while it rises, so his work is positive and the first statement fails. Gravity meanwhile points down against the upward displacement, so its work is negative, making the second statement sound. For a body sliding down an incline friction acts up the slope, opposite to the motion, so its work is negative rather than positive. On a rough floor at uniform velocity the applied force acts along the motion and does positive work, not zero. Air resistance on a swinging pendulum always opposes the bob, so its work is negative. The statements that hold are that gravity does negative work in lifting and that air resistance does negative work on the pendulum.
JEE Main · 2023 · 29 Jan 2023 · Shift 2 · Single correct option