MCAT Physical : Newton's Laws

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

Example Question #1 : General Principles

\(\displaystyle 10g\) ball is rolled into a stationary \(\displaystyle 2g\) ball. If the heavier ball applies a \(\displaystyle 30N\) force on the smaller ball, what force will the smaller ball apply on the large ball?

Possible Answers:

\(\displaystyle -30N\)

\(\displaystyle 6N\)

\(\displaystyle 0N\)

\(\displaystyle 30N\)

Correct answer:

\(\displaystyle -30N\)

Explanation:

The answer to this question lies within Newton's third law: for every action, there is an equal and opposite reaction. If the large ball applies a \(\displaystyle 30N\) force on the smaller ball, the smaller ball will apply a \(\displaystyle 30N\) force on the large ball in the opposite (negative) direction.

Example Question #1 : Newton's Laws

A 1kg plate falls from a shelf 1m above the ground and breaks into three pieces of mass 0.1kg, 0.4kg and 0.5kg. What is the total energy of the scattered pieces?

Possible Answers:

We must know the shape of the plate to solve

\(\displaystyle 9.8 \textup{ J}\)

\(\displaystyle 5 \textup{ J}\)

\(\displaystyle 20 \textup{ J}\)

We must know the velocity of each piece to solve

Correct answer:

\(\displaystyle 9.8 \textup{ J}\)

Explanation:

This is a conservation of energy question. The event is the collision. The initial energy can be calculated by gravitational potential energy:

\(\displaystyle {U = mgh}\)

\(\displaystyle U=(1kg)(9.8\frac{m}{s^2})(1m)=9.8J\)

The final total energy must be the same. The energy of the scattered pieces must add to \(\displaystyle 9.8J\)

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