text: spring force? a 1.3 kg block is dropped onto a relaxed vertical spring that has a spring constant of k=300n/m. the block compresses the spring 12 cm before momentarily stopping.  a) what is the initial height of the block ? b) what work is done on the block by a gravitational force on it while the spring is being compressed ? c) what work is done by the spring force ? d) what is the speed of the block just before it hits the spring ?  e) what is the kinetic energy of the block at the half of the initial height ? read this carefully by conservation of energy total enegy in block remains conserved hence potential enegy at top pt= enegy of spring at bottom pt mgh=1/2kx^2 1.3*10*h=1/2*300*12/100*12/100 h=0.166 m [assuming g=10m/s^2]  b]work done by gravity=1.3*10*12/100                                     =1.56 j  c] work done =-kx                       =-300*12/100                       =-36j  d]potential energy of block at top = k.e. energy before hitting spring  =  mgh=1/2mv^2 10*0.166=1/2*1.3*v^2 v=1.59m/s  e] mgh=mgh/2+1/2mv^2 gh/2=1/2v^2 v^2=1.66 v=1.288m/s