Question

17. What speed must you toss a ball straight up so it takes 4 s to return to you? Be sure to show all work to support your answer.

Answer 1

If we tossed up a coin with some velocity then its acceleration in the air is due to gravity which we can take as a = - 9.8 m/s^2

Also it is given that coin returns to initial position after 4 s

So after 4 s its displacement will become ZERO

now in this process we can say that in whole motion of the coin the net displacement of coin is zero and its acceleration is due to gravity remains constant.

We can use kinematics here

$\Delta y = v_i t + \frac{1}{2} at^2$

$0 = v_i (4) - \frac{1}{2}(9.8)(4)^2$

$v_i = 19.6 m/s$

so approximate speed of the coin must be nearly 20 m/s