A300 g hockey puck is shot across an ice-covered pond. before the puck was hit, it was at rest; after the hit, the puck has a speed of 40 m/s, and comes to rest after going a distance of 30 m. (a) describe how the energy of the puck changes over time, giving the numerical values of any work or energy involved. (b) find the magnitude of the net friction force.

Explanation:

It is given that,

Mass of the hockey puck, m = 300 g = 0.3 kg

Initial speed of the puck, u = 40 m/s

Finally, it comes to rest, v = 0

Distance covered, s = 30 m

(a) We need to find the energy of the puck changes over time. It can be calculated using the work energy theorem as :

W = -240 J

(b) The net friction force can be calculated using the definition of work done.

Since,

F = -8 N

The minus sign shows the friction force as it acts in the opposite direction of motion. Hence, this is the required solution.

it is a negative acceleration