The kinetic energy of a bowling ball is 98 J. Find the mass of the ball if its speed is 7 m / s.

Let’s assume that the bowling ball moves in a closed system. For a closed system, the kinetic energy Ek = (mV ^ 2) / 2, where from the conditions of the problem Ek is the kinetic energy of the ball (98 J), m is the mass of the ball, V is the speed of the ball (7 m / s).
When transforming the formula, we get:
m = 2Ek / V ^ 2 = 2 * 98/7 ^ 2 = 196/49 = 4 kg. Check: kg = ((kg * m ^ 2) / s ^ 2) / (m / s) ^ 2 = ((kg * m ^ 2) / s ^ 2) / (m ^ 2 / s ^ 2) = kg.
Answer: The mass of a bowling ball is 4 kg.