Answer 2_5_8
A coin is dropped from the viewing platform of an observation tower 80 m high. How fast will it travel just before it hits the ground? Why don't you need to know the mass?
Potential Energy = Kinetic Energy
mgDh = 1/2 mv2
m's cancel out
Rearranging: v2 = 2gDh
v2 = 2 x 10 m/s x 80 m = 1600 m2/s2
v = 40 m/s
We don't need the mass as the masses cancel out.