240kg block is dropped onto a spring with a force constant o

2.40-kg block is dropped onto a spring with a force constant of 3.96 times l0^3 from a height of 5.00 m. When the block is momentarily at rest, the spring is compressed by 25.0 cm. Find the speed of the block when the compression of the spring is 15.0 cm.

Solution

total mechanical energy of spring-block system: T.E =1/2*k*d^2 =0.5*3960*0.25^2=123.75J

=>when x=0.15m

=>1/2*3960*0.15^2+0.5*2.4*V^2=123.75

=>0.5*2.4*V^2=79.2 =>V^2=66=>V=8.124m/s