A spring store 5J of energy when stretched by 25cm. It is kept vertical with the lower end fixed. A block fastened to its other end is made to undergo small oscillation. If the block makes 5 oscillation each second, what is the mass of the block?
x=25cm=0.25m
E=5J
f=5
So, T=1/5sec
Noe P.E. =(1/2)kx2
⇒(1/2)kx2=5⇒(1/2)k(0.25)2=5⇒k=160N/m
Again, T=2π√mk⇒15=2π√m160⇒m=0.16kg.