Physics 11th grade 2
posted by Isis .
1) A 20 kg rock is on the edge of a 100 m cliff.
a. What potential energy does the rock possess relative to the base of the cliff?
b. The rock falls from the cliff. What is the kinetic energy just before it strikes the ground?
c. What speed does the rock have as it strikes the ground?
2) Justin pulls his 55 kg girlfriend in a 12 kg sled with a constant force of 79 N for 120 meters.
a. How much work did Justin do moving his girlfriend?
b. How much power did he expend if it took him 4 minutes to move this distance?

1) PE = mgh
PE = 20 kg * 9.8 m/sec^2 *100m
KE = PE
KE = 1/2 * m*v^2
2) W=F x d
F = mg
Force = 55 x 9.8 m/sec^2 
Number two is way off the mark.
work=force*distance=79*120 joules