Question

You push a hockey puck that is initially at rest on slick ice by applying a constant force until the puck reaches a final velocity of 1 m/s. On the second attempt, you want the hockey puck to reach the same final velocity by applying a force that is twice as large.
1. Therefore, you must exert the force for a time interval that is
A. shorter than the time interval of your first attempt.
B. longer than the time interval of your first attempt.
C. the same as the time interval of your first attempt.
2. After the hockey puck has reached the final velocity, you suddenly stop pushing it. The hockey puck:
A. stops abruptly
B. reduces speed gradually
C. continues at constant velocity
D. increases speed gradually
E. reduces speed abruptly

Answer 1

Answer:

1. A

2. B or C

Explanation:

1.

F=ma, meaning that if you use two times more force on a constant mass, the acceleration must double. Acceleration is change in velocity, which means that if you are aiming for the same final velocity the change must happen in half of the time. Therefore, the correct answer is choice A.

2.

By Newton's first law, an object in motion will stay in motion unless an external force acts on it. Since there is nothing pushing the puck in the other direction, the puck will either keep on going for at a constant velocity or will reduce its speed gradually, depending on whether or not this ice is considered to be frictionless. Hope this helps!