Final answer:
The kinetic energy of a ball moving at 4m/s with a mass of 7kg is 56 J.
Step-by-step explanation:
The kinetic energy (KE) of an object can be calculated using the formula KE = 1/2 * mass * velocity^2. Given that the mass of the ball is 7kg and its velocity is 4m/s, we can substitute these values into the formula:
KE = 1/2 * 7kg * (4m/s)^2 = 1/2 * 7kg * 16m^2/s^2 = 56 J
Therefore, the kinetic energy of the ball is 56 J, which corresponds to option c.