Ethan a 70 kg ice hockey goalie who is originally at rest is...

Ethan, a 70-kg ice hockey goalie who is originally at rest, is hit by a 0.12-kg ice hockey puck that is traveling at a velocity of 37.2 m/s. Ethan hits the puck in such a way that this may be considered an elastic collision. Calculate the speed of the goalie after he hits the puck. a. 31.5 cm/s b. 16.4 cm/s c. 22.2 cm/s d. 36.2 cm/s e. 12.7 cm/s

Transcript

00:01 In the given problem we have a 70 kg ice hockey goalie who is initially at rest and catches a 0 .150 kg hockey puck coming to him at 33 meters per second.

00:11 So we will assume m1 is the mass of the hockey goalie it will be 70 kgis and he is initially at rest hence its initial velocity let it be u1 will be equal to 0.

00:22 Mass m2 of the puck will be 0 .150 kg and it is coming at initial velocity u2 equal to 33 .0 meters per second so we have to find what type of collision is this and why so as the puck and the goli initially are individual bodies but after catching it the golly will catch the puck and both of them will move at the same velocity therefore it is an inelastic collision so in inelastic collision we have to find if there is a conservation of momentum or conservation of kinetic energy in this only conservation of momentum is valid because kinetic energy is not conserved in inelastic collisions now we have to find the recoil velocity of the same ice hockey goalie who is initially at rest and it it catches the same hockey puck but it is coming at the velocity vu2 equal to 35 .0 meters per second.

01:36 So if the conservation of momentum is valid in this case we can write that m1 u1 plus m2 u2 will be equal to m1 plus m2 v.

01:48 Here left -hand side is the initial momentum and right -hand side is the final momentum.

01:53 So we need to calculate the final velocity v it will be equal to m1 u1 since the initial velocity of the hockey goal is 0 this first term will be equal to 0 hence the final velocity will be equal to m2 u2 divided by m1 plus m2 we have the mass of the puck as 0 .150 kg and it is coming at a velocity of 35 meters per second divided by the mass of both of them it will be 0 .15 kg plus 70 kg so we have velocity v equal to 0 .05 meters per second.

02:37 Now we need to calculate the difference in the kinetic energy.

02:41 So let it be denoted by delta k.

02:45 It will be the final kinetic energy minus the initial kinetic energy...

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