energy science math

Question

John is a crane operator and drops his 0.025 kg wallet out of the window of his crane. When the wallet is 21.5 m from the ground it has a total mechanical energy of 2.26x10^1J. What is the wallets kinetic energy?

Answer 1

height=21.5

mass=0.025kg

total mech energy=22.6J

The total mechanical energy is the sum of the potential energy and the kinetic energy. If we figure out the potential energy using the height, mass, and gravity, we can subtract that from the mech energy to find the kinetic energy.

PE=mgh

PE=0.025kg*9.8m/s^2*21.5m

PE=5.2675kg*m^2/s^2

PE=5.2675J because J is equal to kgm^2/s^2

TME-PE=KE

22.6J-5.2675J=17.3325J

KE=17.3 J Rounded down to significant digits