Question

Starting from rest, a man runs 10 metres along a straight path in t seconds. His position can be described by the function s(t)=0.7t^2. How long will it take him to reach the velocity of 4m/s?

would the answer be 5.6 s? I started with s(t)=0.7t^2, then the velocity is 7/5t and then I substituted 4 into t.

Answer 1

s = .7 t^2
ds/dt = v = 1.4 t
4 = 1.4 t
t = 4/1.4 = 2.86 seconds

It asked for t given v = 4 m/s

Answer 2

thanks!