# How long until the ball hits the ground?

by hyde2042
Tags: ball, ground, hits
 P: 25 1. The problem statement, all variables and given/known data A ball is thrown downward from a height of 30m at 8m/s. How long until it hits the ground? (Air resistance is negligible and gravity is 9.8m/s 2. Relevant equations I tried deltaX=Vi+(1/2)a(t^2) and came out with 2.12, but the solution says it's 1.79. 3. The attempt at a solution 30=8+(1/2)(9.8)(t^2) 22=4.9(t^2) sqrt4.49=sqrt(t^2) t=2.12
 Sci Advisor HW Helper P: 4,301 Are you not missing a t? $$V = V_i + a t$$ so $$\Delta x = V_i \mathbb{t} + \frac12 a t^2$$
 P: 25 Thank you, but I'm afraid I'm evenb more confused by the additional t. I ended up at 30-8t=4.9(t^2) What I keep doing after that seems to make it more complicated than it should be. COuld you possibly point me in the right direction? Thank you for your time.
HW Helper
P: 4,301

## How long until the ball hits the ground?

It's a standard quadratic equation, of the form ax2 + bx + c = 0.
How do you solve one of those?
 P: 25 Ah... hate when I over look simple things. Thank you very much.

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