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?

As per Newton's III law every action has equal and opposite reaction.

Explanation:

When Kamala apply force on the wall then equal and opposite force is applied by the wall on Kamala

Due to this reaction force of the wall Kamala moves on her skates in backward direction

Now if Kamala push the wall hard then the reaction force on kamala will be more in magnitude due to which she will roll backward will greater speed as we know that

F = ma

if the reaction force is more then the acceleration will be more so Kamala will roll backward with greater speed

float.

archimedes' principle

denser than water sinks in water.

denser than mercury would sink in it