Practice Problem: Inelastic Collisions at the Skating Rink

Practice Problem: Inelastic Collisions at the Skating Rink


You and your friend decide to spend the afternoon
at the ice skating rink, but to mix things up, you decide to bring a 0.2 kilogram frisbee. Much to the irritation of the other patrons
at the rink, you begin to toss the frisbee back and forth as you skate around. Given that you are both really into physics
right now, you try an experiment. You stand perfectly still, while your friend
tosses you the frisbee as hard as they can, which turns out to be twenty meters per second. When you catch the frisbee, assuming the ice
is frictionless, you and your seventy kilograms of mass are propelled backwards, but with
what velocity? To figure this out, we just need equations
regarding collisions, since we can consider catching a frisbee a collision of sorts. Check out my tutorial on this subject if you
need to, and then see what you come up with. As we said, when you catch the frisbee, we
can regard this as a collision, and more specifically an inelastic collision, as the frisbee doesn’t
bounce off of you, but rather, you and the frisbee become one object moving together. The equation regarding inelastic collisions
tells us that M one V one plus M two V two equals the quantity M one plus M two times
V final. So let’s just plug in everything we know. Taking you to be object one, your initial
velocity was zero, so we can just get rid of this term. The frisbee has a mass of 0.2 kilograms, and
was moving at a speed of twenty meters per second. Then over here, we can add the two masses
to get 70.2 kilograms, and then solve for the final velocity. That will give us 0.057 meters per second. This is pretty small of course, given the
huge difference in mass between you and the frisbee, but it’s still a pretty interesting
way to get across the ice.

5 thoughts on “Practice Problem: Inelastic Collisions at the Skating Rink

  1. haha aww man where was this video a few months ago before my physics exam! These problems gave me a bit of a headache at times. Still, managed to get a fantastic mark overall and I a lot of that to you, so thank you for your excellent channel 🙂

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