Final answer:
The energy of the hockey puck changes over time: Initially, the puck has no kinetic energy, but when it is hit, work is done to give it kinetic energy. The puck comes to a stop due to the net friction force acting against its motion. The magnitude of the net friction force is 240 N.
Step-by-step explanation:
The energy of the hockey puck changes over time during its motion across the ice-covered pond. Initially, the puck has no kinetic energy since it is at rest. However, when it is hit, work is done on the puck to give it kinetic energy. The amount of work can be calculated using the work-energy theorem, which states that the work done on an object is equal to the change in its kinetic energy. In this case, the work done on the puck can be calculated as:
Work = (change in kinetic energy) = 1/2 * mass * (final velocity)^2 - 1/2 * mass * (initial velocity)^2
Substituting the given values, we have:
Work = 1/2 * 0.300 kg * (40 m/s)^2 - 1/2 * 0.300 kg * (0 m/s)^2
Work = 240 J
As the puck moves across the pond, it comes to a stop due to the net friction force acting against its motion. The magnitude of the net friction force can be determined using the work-energy theorem again. The work done by the friction force is equal to the change in the puck's kinetic energy. Since the puck comes to rest, its final kinetic energy is 0.
Work = (change in kinetic energy) = - 1/2 * mass * (final velocity)^2 - (- 1/2 * mass * (initial velocity)^2)
Substituting the given values, we have:
- 240 J = - 1/2 * 0.300 kg * (0 m/s)^2 - (- 1/2 * 0.300 kg * (40 m/s)^2)
- 240 J = - 1/2 * 0.300 kg * (-1600 m/s^2)
- 240 J = 240 J
The negative sign indicates that the work is done against the motion of the puck. Therefore, the magnitude of the net friction force is 240 N.