Question

You are watching a hockey game on your digital video recorder. Your team's goalie is at rest when he catches a 0.18-kg puck moving straight toward him. The announcer says it was a 35 m/s slap shot, based on radar gun data. Normally the goalie would be braced, but in this case he is resting on parallel skate blades so that there is negligible friction to impede his subsequent motion. The collision is too fast to observe quantitatively, but by running the video in slow motion, you can tell that the goalies glove is 150 mm from his body when the puck strikes and is right against his chest after the successful catch. It is also clear that the stunned goalie (holding the puck) drifts backward at 71 mm/s for a second or two after the collision is over. The direction of the pucks initial velocity is the +x direction.

Part A
Compute the average acceleration of the puck during the collision.

Part B
Compute the average acceleration of the goalie during the collision.

Part C
Determine the inertia of the goalie (including his equipment).

Part D
How much kinetic energy is converted to thermal energy in the glove

Answer 1

(a)

a = v² - u² / (2d)

a = 0.071² - 35² / ( 2 * 0.15)

a = - 4083.32 m/s²

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(b)

time for this acceleration to occur

v = u + at

t = v - u / a

t = 0.071 - 35 / 4083.32

t = 8.554e-3 seconds

so,

acceleration of goalie

a = 0.071 / 8.554e-3

a = 8.3 m/s²

______________

(c)

does inertia means mass here ???

m (goalie) / m ( puck) = a ( puck) / a (goalie)

m (goalie) = 0.18 *4083.32 / 8.3

m (goalie) = 88.55 kg

_____________________

(d)

E = initial kinetic energy - final kinetic energy

E = 1/2 * 0.18 * 35² - ( 1/2 * 88.55 * 0.071² + 1/2 * 0.18 * 0.071² )

E = 110 J