Question

#14 Question: Unless otherwise stated, all objects are located near the Earth's surface, where g = 9.80 m/s2 .
A hockey puck impacts a goalie's plastic mask horizontally at 120 mi/h and rebounds horizontally off the mask at 50 mi/h .

-If the puck has a mass of 172 g and it is in contact with the mask for 29 ms , what is the magnitude of the average force that the puck exerts on the mask?

-Assuming that this average force accelerates the goalie (neglect friction with the ice), with what speed will the goalie move, assuming she was at rest initially and has a total mass of 78 kg ?

Answer 1

Initial velocity u = 120 mi/h

u = 120 X 1609.34 m/ 3600 s

u = 53.65 m/s

Velcoity after rebounding v = - 50 mi /h

v = - 50 X 1609.34 m/ 3600 s

v = - 22.35 m/s

time t = 29 ms = 0.029 s

Change in momentum of puck = mv - mu

Change in momentum of puck = m( v - u )

Change in momentum of puck = 0.172 ( -22.35 - 53.6) = -13.06 Kgm/s

Average force = change in momentum / time

F = -13.06/.029

F = -450.3

so only taking magnitude

F = 450.3 N

acceleration of goalie

a = F/m

a = 450.3/78

a = 5.77 m/s²

Initial velocity u = 0

t = 0.029 s

using first equation of motion

v = u + at

v = 0 + (5.77)(0.029)

v = 0.17 m/s