posted by kelly .
1.A 75 kg passenger in a van is wearing a seat belt whent he van moving at 15m/s, collides with a conrete wall. The front end of the van collapses 0.50 m as it comes to rest.
a) what was the paseenger's kinetic energy before the crash
b) What average force did the seat belt exert on the passengfer during the crash?
2. A 1400 kg car is accelerating up a hill. The hill is 150m long and the total rise of the hill is 6.0m. The car accelerates from a speed of 7.0m/s at the bottom to 15m/s at the top. If the average retarding force of friction is 700 N find the change in potential energy of the car, and the change in kinetic energy of the car.
KE=1/2 m v^2
2. change in PE= 1400*g*6m
change in PE=finailKE-initialKE
= 1/2 m (15^2-7^2)