Question

Ray weighs 100 kilograms, his wrestling partner, Bobby, weighs 50 kilograms. If Ray moves at 4 m s , how fast will Bobby have to run at him to apply an equal amount of kinetic energy?

Answer 1

Both Ray and his wrestling partner have kinetic energy by virtue of them moving. Ray has a mass
`m=100kg` , velocity
`v=4m/s`. Ray's kinetic energy is calculated as follows,

`KE=(1)/(2) mv^2=(1)/(2) * 100kg* (4m/s)^2=800 J.`

Bobby wishes to archive the same amount of kinetic energy as Ray. To find what his velocity should be, we have to solve for
`v` in the kinetic energy formula. For Bobby,
`KE=800J`, mass
`m=50kg`.

So,

`KE=(1)/(2) mv^2\\=>800J=(1)/(2) * 50v^2\\=>v^2=(1600J)/(50kg) \\\\=>v=\sqrt{(1600J)/(50kg)} =5.66m/s` .

This means for Bobby to have the same kinetic energy as Ray, he has to run at
`5.66m/s.`