Submit a question to our community and get an answer from real people.

KE energy question?

The goblins fists cut through the air and connects with the dwarfs face in an elastic collision. The goblins fists each weigh 2kg and the dwarfs head weighs 5kg. What is the kinetic energy imparted to the dwarfs face by the goblins fists if the goblins fists had an initial velocity of 5m/s?

I used the formula KE= 1/2mv^2 but I don't think thats it.

Report as

With a perfectly elastic collision, both linear momentum and kinetic energy are conserved. It's possible you have already seen the equations worked out under these conditions, and can use them. If not (and even if so and you want to get better understanding) write down the conservation equations. That is write down the equation conserving linear momentum, and the equation conserving kinetic energy. You should have these two equations being of two unknowns (final velocities). Thus you will have a finite set of solutions. Solve them simultaneously. You can then calculate the kinetic energy of either body using the formula posted. With the given problem, you should treat the two fists as one body with the sum of the fist's masses.