Work by a Constant Force
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 is zero.
E. Work done by the air resistance on an oscillating pendulum is negative.
Choose the correct answer from the options given below:
Show answer and solution
Answer: (d)
- A: the man pulls up and the bucket moves up, so his work is positive. False.
- B: gravity acts down, bucket moves up, so its work is negative. True.
- C: friction opposes the sliding, so its work is negative. False.
- D: applied force is along the motion (balancing friction), so its work is positive. False.
- E: air resistance always opposes the motion, so its work is negative. True.
- So the answer is (d) B and E only.