A 10g bullet travelling at 400m s−1 is brought to rest in 0.003s when it enters a wooden block. An identical bullet with the same initial speed is brought to rest in 0.006s when it enters sand. What is the ratio of the magnitudes of the average retarding forces exerted by the wood and the sand respectively?
a) 1:2
b) 4:1
c) 2:1
d) 1:1