Internal and Kinetic Energy.
1. The problem statement, all variables and given/known data
A 14.0 kg block is dragged over a rough, horizontal surface by a 78.0 N force acting at 20.0° above the horizontal. The block is displaced 5.00 m, and the coefficient of kinetic friction is 0.300.
(a) What is increase in internal energy of the block-surface system due to friction?
(b) Find the total change in the block's kinetic energy.
2. Relevant equations
(a) Fk=(coefficient of kinetic friction)(mass)(gravity)
Change in energy=(Fk)(displacement)
(b) Change in K= Work of other forces - Change in energy
3. The attempt at a solution
(a)Fk=(coefficient of kinetic friction)(mass)(gravity)=(.3)(14)(9.8)=41.16
Change in energy=(Fk)(displacement)=41.16(5)=205.8J
(b)Change in K= Work of other forces - Change in energy
= (78.0)(5)(cos20)
= 366.5 - 205.8=160.7J
however, these answers are wrong..? Suggestions?