# Physics Kinematics Question

Discussion in 'MCAT Study Question Q&A' started by Boomie, Jun 14, 2008.

1. ### Boomie

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This is a test prep practice question. I have not been able to figure out the calculations.

A baseball is thrown vertically with a speed of 3m/s. Find the total distance that the ball has been in flight when it has traveled 50cm.

The answer is 0.398 seconds. But I can't figure out how to solve the problem.

I converted 50cm to 0.5m.
I used the formula for linear motion equation: X-X0 = V0 t + (at^2)/2.
Where V0+ 3 m/s
a= 9.8 m/s2
and X-X0 = 0.5 meters

From here it should just be plugg and chugg but I am not getting it right...

Can someone please work out the problem for me. Or tell me if I am using the wrong equation to try and solve this problem.

Thank you..

3. ### bluemonkey

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Did you use the correct signs for your initial velocity and acceleration vectors? Are they in fact in the same direction? You should arrive at the correct answer once you answer these questions...

4. ### cwfergus

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You did it right. X= Xo + Vot + .5at^2

where x=0.5 Xo= 0, Vo= 3, a=-9.8

0.5= 0 + 3t + -4.9t^2

-4.9t^2 + 3t - 0.5 = 0

-b +/- sqrt( b^2 - 4ac) / 2a

you come out with

0.306 +/- -0.092
So we have either 0.398 or 0.214

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