Question

Unless otherwise stated, all objects are located near the Earth's surface, where = 9.80m/s^2 .
A hockey puck impacts a goalie's plastic mask horizontally at 128mi/hr and rebounds horizontally off the mask at 49mi/hr .

If the puck has a mass of 180g and it is in contact with the mask for 26ms , what is the magnitude of the average force that the puck exerts on the mask?

Answer 1

The impulse formula gives you everything you need.
\[F \Delta t = m \Delta v\]

Answer 2

I don't get the right answer when I use that formula though.

Answer 3

What did you get for delta v?

Answer 4

I converted both of the velocities to m/s and when I subtracted them I got -35.32

Answer 5

Delta v in mph is 128-(-49) = 177 mph. Convert that to m/s. Make sure you use 0.18 kg, and try again.

I have to leave for ~30 min.

Answer 6

I must have messed up my conversions somewhere. Anyway, I found the the correct answer. Thank you so much for your help!! :)

Answer 7

Okay I have another one for you.
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 77kg ?

Answer 8

We have to use different formulas for lady hockey.

\[m _{p} \Delta v _{p}=m _{g}\Delta v _{g}\]

The total change in momentum has to be zero.

Answer 9

I don't understand what to plug in.

Answer 10

The change in the puck momentum is equal and opposite to the change in the goalie momentum. s

Answer 11

If you know the puck momentum, then that is the goalie momentum. Just divide out her mass to get velocity.

Answer 12

Solve the equation for delta v sub g (the velocity of the goalie), and fill in the variables.

Answer 13

What is delta v sub g though. Like how do I solve that?

Answer 14

That's the change in velocity of the goalie.

Answer 15

\[\Delta v _{goalie}=\frac{ m _{puck}\Delta v _{puck} }{ m _{goalie} }\]