Question

question 16 (4 points)
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an engineering student is conducting an investigation on the motion of a model car travelling down a ramp. after the first trial, the student calculates that the kinetic energy at the bottom of the ramp is greater than the potential energy at the top of the ramp. which of the following can best explain the difference?
the car’s mass increased as it moved down the ramp.
there was friction on the ramp that converted some kinetic energy to thermal energy.
the measured height of the ramp was greater than the actual height.
the student accidently pushed the car forward at the top of the ramp.

Explanation:

1. Analyze Option A: Mass of an object is constant (assuming no mass gain/loss), so the car’s mass can’t increase moving down the ramp. Eliminate A.
2. Analyze Option B: Friction converts mechanical energy (kinetic/potential) to thermal energy, which would decrease kinetic energy at the bottom (since energy is lost to heat), not make it greater than initial potential energy. Eliminate B.
3. Analyze Option C: If measured height > actual height, calculated potential energy (\(PE = mgh\)) would be higher than actual. But the problem states kinetic energy (KE) at bottom > calculated PE (from measured height). If actual height is less, actual PE is less, but this doesn’t explain KE > PE. Eliminate C.
4. Analyze Option D: If the student pushed the car at the top, the car gains initial kinetic energy (from the push) in addition to the kinetic energy from converting potential energy. So total KE at bottom = KE from push + KE from PE conversion, which could make KE > initial PE (since initial PE only accounts for gravitational potential, not the push’s KE). This explains the difference.

Answer:

D. The student accidently pushed the car forward at the top of the ramp.