Ok, I thought I knew how to do this, but for some reason, according to my homework website, my answer is wrong. So I'm turning to this board before I beat my head against the wall. Please help me.(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

A ball is thrown with an initial speed of 31 m/s at an angle of 45�. The ball is thrown from a height of 12 m and lands on the ground.

Find the time of flight.

3. The attempt at a solution

Initial vertical upward velocity = 31 sin 45 = 26.378m/s.

The displacement [Yf – Yo] = –12 m

Yf -Yo = Vot - 0.5*g*t^2

–12 = 26.378 t – 4.905 *t^2

4.905 *t^2 – 26.378 t – 12 = 0

--------------------------------------...

Using b^2 – 4ac = 26.378 ^2– 4*4.905*(– 12)

√ (b^2 – 4ac) = 30.516

– b ±√ (b^2 – 4ac) = 26.378 ± 30.516

= 56.894 leaving the negative time value

Dividing by 2a = 9.81

t = 5.7996 s

Is my work right?

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# Homework Help: Projectile motion

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