# Balls - Projectile

1. Feb 7, 2005

The balls are released from rest at a height of 5.0m at time t=0s. How long $$t_g$$ does it take for the balls to reach the ground? Use 10 m/s^2 for the magnitude of the acceleration due to gravity.

i'll use the position formula for this problem:

$$y = y_0 + V_{y_0}*t - 1/2*g*t^2$$

well i know that
$$y_0$$ = 5.0 m
g = 10 m/s^2

i'm missing $$V_{y_0}$$

if i plug in t = 0, wouldnt it just cancel everything out? but it doesnt make sense.

2. Feb 7, 2005

### mikeu

The balls are released from rest, which tells you that their initial velocty $$V_{y_0}$$ is zero. If you plug in t=0 you just get $$y=y_0$$, or 5.0 m, which just tells you that the balls do in fact start where they start (always a good check ).

What you want to do to solve the problem is find out what value of t will give you $$y=0$$, since that's the 'height' of the ground.