A 15,800 kg truck is moving at 12 m/s when it starts down a 3 o incline in the C

Question

A 15,800 kg truck is moving at 12 m/s when it starts down a 3o incline in the Canadian Rockies. At the start of the descent, the driver notices that the altitude is 1630 m. When she reaches an altitude of 1440 m, her speed is 28 m/s.
(Note: answer the 'change' questions below with signs appropriate to 'delta' conventions.)

a.) Find the change in the truck's gravitational potential energy.
  J
(I cannot find the answer to part a)

b.) Find the change in the truck's kinetic energy. (5056000J, I inputted this and this is correct)
J

Explanation / Answer

a) the change in the truck's gravitational potential energy:

dU = mgh = 15800*9.8*(1440 - 1630) J = -29419600 J

b) the change in the truck's kinetic energy:

dK = Kf - Ki = 0.5 *15800*(282 - 122) J = 5056000 J

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