During the last seconds of a hockey game, the losing team replaces their goalie

Question

During the last seconds of a hockey game, the losing team replaces their goalie with a good shooter. The other team shoots the 150-g puck with an initial speed of 7.0 m/s directly toward the unguarded net from a distance of 32 m. The coefficient of kinetic friction for the puck on the ice is 0.08. a) what is the force of kinetic friction acting on the puck? b) what is the acceleration of the puck? c) how long does it take the puck to stop? d) will the puck reach the net if no other player touches it? Please show your work. Answers are... a) 0.1 N b) -0.8 m/s^2 c) 9s d) no

Explanation / Answer

part a:

normal force on the puck=weight of the puck=mass*g

=0.15*9.8=1.47 N

then kinetic friction force=friction coefficient*normal force

=1.47*0.08=0.1176 N

part b:

acceleration of the puck=kinetic friction force/mass

=-0.1176/0.15=-0.784 m/s^2

(-ve sign is because of the fact that friction fore is opposite to the direction of motion)

part c:

initial speed=7 m/s

acceleration=-0.784 m/s^2

final speed when it stops=0

then time taken to stop=(final speed-initial speed)/acceleration

=(0-7)/(-0.784)=8.928 seconds

d)distance covered before the puck stops

=initial speed*time+0.5*acceleration*time^2

=7*8.928-0.5*0.784*8.928^2

=31.25 m

hence it wont reah the net.

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