Question

kamala puts on inline skates and stands facing a wall. when she pushes against the wall, she rolls backward. why does pushing harder make her roll faster?
the force of friction between the wheels and the ground decreases.
the force of the wall pushing on her increases.
the additional force decreases her weight.
the extra force causes an increase of the normal force from the ground.

Explanation:

To determine why pushing harder makes Kamala roll faster, we analyze each option:

• Option 1: Friction between wheels and ground is related to normal force (not directly to pushing the wall). Pushing harder on the wall doesn't decrease this friction. Eliminate.
• Option 2: By Newton's third law, when Kamala pushes the wall harder, the wall pushes her with an equal and opposite force. A larger push on the wall means a larger reaction force from the wall, which accelerates her more, making her roll faster. This makes sense.
• Option 3: Pushing the wall doesn't change her weight (mass × gravity, mass and gravity are constant here). Eliminate.
• Option 4: The normal force from the ground is related to her weight (in vertical direction), and pushing the wall is a horizontal force. It doesn't directly cause an increase in normal force. Eliminate.

Answer:

The force of the wall pushing on her increases.