Question

A block of mass `5kg` is being raised vertically upwards by the help of a string attached to it. It rises with an acceleration of `2ms^-2`. Find the work done by the tension in the string if the block rises by `2.5m`. Also find the work done by the gravity and the net work done.

Answer 1

Let us first calculate the tension. From figure
`T-mg=5a`, `T=5(10+2)=60N`
As T and displacement are in same direction (upwards), work done by the tension T is W.
`W=Ts=60(2.5)=150J`
Work done by gravity
`=-mgs=-5(10)(2.5)=-125J`
Net work done on the block= Work done by T+Work done by `mg`
`=150+(-125)=25J`