If a stone is thrown down at 100 ft/s from a height of 1,150 feet, its height after t seconds is given by s = 1,150 - 100t - 16t2.

Question

(a) Find its average velocity over the period [1, 2].
ft/s

(b) Estimate its instantaneous velocity at time t = 2. HINT [See Example 3.]
ft/s

Answer 1

You have an equation for the position at any time. Find the position at t=2 and subtract the position at t=1

s(2) - s(1) = the displacement.The average velocity is defined to be the displacement / time interval. You should have [ s(2) - s(1) ] / (2 -1)

That solves the average velocity for part A

For part B, you should use the kinematic equation v = V_0 + at