Answer:
(a) The force changes its magnitude with respect to displacement, hence the total work will be sum of increment of work in three steps:-
step 1 . from 0 to 0.25m .
force = 0.6 N
displacement= 0.25m
work done =( force × displacement) = (0.25 × 0.6 ) = 0.15 joule.
step 2:- .
work done in moving from 0.25 to 0.50 m.
work done = ( force × displacement) = ( 0.4 × 0.25) = 0.10 Joule. .
step 3 :-
work done in moving from 0.50 to 0.75 m
work done = 0.8 × 0.25 = 0.200 joule.
hence total work done = ( 0.20+0.10+0.15) = 0.45 joule. ans
(b) similar concept you have to use here also.
step 1:
from 0.20 to 0.50, force of magnitude 0.4 N acts on the object.
Work done = ( 0.50-0.20)× 0.4 = 0.30 × 0.4 = 0.12 joule.
step :- 2
from 0.50 to 0.55 , force of magnitude 0.8 N acts on the block.
work done = 0.8× ( 0.55- 0.50) = 0.04 joule
total work done = 0.04 + 0.12 = 0.16 joule. ans
