Answer:
Step-by-step explanation:
a )
One of the pulley is fixed and the other is moving . From the moving pulley load of 20 kg is hanging . One end of the cord is fixed from ceiling and the other end is free. Let T be tension in the whole cord. T will be the force applied by me.
Since cord is wrapped around the moving pulley , 2T will balance the weight of load.
2T = mg
T = mg / 2
= 20 x 9.8 / 2
= 98 N .
b )
If weight moves upward by 2 cm , cord on either side of load becomes loose by 2 cm . So the free end of cord moves by 4 cm .
so free end has to be pulled by 4 cm .
c )
force applied by me = T
= 98 N
displacement = 4 cm
= .04 m
work done = force x displacement
= 98 x .04
= 3.92 J.
d )
work done by gravitation
= mg x - d
= 20 x 9.8 x - .02
= - 3.92 J ( work done will be negative as direction of displacement is opposite to direction of force by gravity ).