Question

A wagon slides down a hill with friction between the wagon and the ground but with negligible air resistance. Which of the following must be correct about the resulting change in energy of the wagon-earth system?

a. The sum of the kinetic energy and the gravitational potential energy changes by
an amount equal to the energy dissipated by friction.
b. The gravitational potential energy decreases and the kinetic energy is constant.
c.The decrease in the gravitational potential energy is equal to the increase in
kinetic energy.
d. The gravitational potential energy and the kinetic energy must both decrease.

correct answer is A. why is A correct and why are the other answers incorrect?

Answer 1

Below

Step-by-step explanation:

The question asks which MUST be correct

B MIGHT be correct, but likely the wagon is accelerating so KE is INCREASING as it goes down the hill

C Not true because some energy is lost due to friction

D KE is increasing (see B above) while PE is decreasing as it is lowered

Answer A

At top all energy is PE

at bottom the PE has been changed to KE and frictional losses