Work done by the force of friction is____________________?
Correct answer: B. always negative
- A. always positive
- B. always negative
- C. positive only for small frictional force
- D. positive only for large frictional force
Explanation
For ordinary friction opposing the motion, the angle between friction and displacement is 180°, so W = Fs cos 180° = -Fs, making the work negative. The likely wrong choice is c because the sign of frictional work does not depend on whether the frictional force is small or large.
Last updated
About Work
Work is done when a force produces displacement, with its value determined by the component of force along the displacement. The topic covers positive, negative and zero work, work by variable forces from force-displacement graphs, and the connection between net work and change in kinetic energy.
Practise Work and Energy
748 free Work and Energy MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Exams that ask Physics questions like this
Physics is on 13 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
Related questions
A 1.75 m tall weight-lifter raises a weight of mass 50 kg to a height of 0.5 m above its head. How much work is being done by it? (g = 10 ms-2)
A 10 N force moves a body around a circular path of radius 50 cm. What is work done in completing one revolution?
A 10N force moves a body around a circular path of radius 50 cm. What is work done completing one revolution?
A 4kg eagle picks up a 75g snake and raises it 2.5 m from the ground to a branch. What is the workdone by the eagle on the snake? (g=10m/s2)
A 50kg man with a 20kg load on his head climbs up 20 steps of 0.25m height each. The work done in climbing is?