Suppose you throw a small rock over a lake so that it sails over the surface of the water. The rock has a mass of 0.090 kg and is initially moving at 8.0 m/s. How much net force does it take to bring the rock to a stop in 1.00 s?
m = 0.09 kg v o = 8 m / s v = v o - a t v = 0 m/s ( velocity is zero when the rock stops ) 0 = 8 - a 1 a = 8 m/s² F = m a F = 0.09 kg * 8 m/s² = 0.72 N Answer: C ) 0.72 N
