(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data[/

A ball is thrown directly downward, with an initial speed of 7.15 m/s, from a height of 31.0 m. After what time interval does the ball strike the ground?

2. Relevant equations

All the kinematics equations dealing with velocity and height and accelration. need to solve for time.

3. The attempt at a solution

I tried this one couple of times. The first thing I did was use the equation Yf=Yi+Viyt+1/2(a)t^2.

I chose the top to be postive.

0= 31.0m+ 7.15 m/s(t)+1/2(-9.80)t^2

I saw that this look like a qudratic equation so i work it out

ax+bx+cx

-7.15 m/s +/-[(-7.15-4(-4.90)(31.0)/2(-4.90)]^1/2

it came out to be

-7.15+7.53 = 0.38

-7.15-7.53= -14.68

i think im not doing something right, need some help with this one.

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# Free Falling Object question

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