What is the mass of an object travelling at 15 m/s with a kinetic energy of 100 J?

Kinetic Energy (E_k) = 1/2(mv²).This can be rearranged such that, m = (2E_k)/v²we know from the question that E_k = 100 J and we know that v = 15 m/sso plugging in the numbers, we get m = (2 x 100)/(15)² = 200/225 = 0.89 Kg (to 3 significant figures)