Projectile Motion

Question

Someone in a car going past you at the speed of 39 m/s drops a small rock from a height of 1.5 m. How far from the point of the drop will the rock hit the ground? The acceleration due to gravity is 9.8 m/s 2 . Answer in units of m.

Answer 1

Hi Charlie P.,

Using y = y₀ + v_y*t + a*t²/2 for the vertical fall (positive y-direction up), and x = v_x*t for the horizontal distance. v_x = 39 m/s; y₀ = 1.5 m; v_y = 0; a = 9.8 m/s², we get:

0 = 1.5 - 4.9*t²

t² = 1.5/4.9

t = 0.55328 s

x = v_x*t = 39*0.55328 = 21.6 m

I hope this helps, Joe.