mgsin37°-µmgcos37°=ma
a=g(sin37°-µcos37°)
L=1/2 at² =1/2 at² =2a (t=2)
h=Lsin37°=2asin37°
W=mgh
=mg(2asin37°)
=2mg²(sin37°-µcos37°)sin37°
=2×2×10²(0.60-0.5×0.80)×0.60
=400×0.20×0.6
=80×0.6
=48(J)