The mass of an object with 500j of kenetic energy moving with a velocity of 5 m/s is

Kinetic energy = k.E = 500
velocity  = V=  5
mass = M =?
K.E = 1/2 x (M)(V*2)
500 = 1/2 x (M)(5*2)
500 x 2 = M x (25)
1000 /25  =  M
M =  40 kg

Answer sample (c); // would be best because the percentage of the energy in an incident wave that remains in a reflected wave from this material is the smallest;