Question

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?

A. 89 N

B. 0.120 N

C. 0.72 N

D. 0.011 N

Answer 1

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 

Answer 2

The answer is C. 0.72 N.