(a) Give two conditions for work to be done. (b) What is the work done by frictional force on an object when dragged along a rough surface ? (c) Relate power and work. (d) A machine does 1960 joule of work in 4 minutes. What is the power?

CBSE Class 9 CBSE Class 9 Science
1

(a) A force should act on the body and it should have displacement.
(b) Negative.
© P = work/time
(d) Given W = 1960 J, t = 4 min = 4 x 60 = 240 s,
P = ?
P = W/t = 1960/240 = 8.2 W