Initial Velocity Question


by bwilhelm
Tags: initial, velocity
bwilhelm
bwilhelm is offline
#1
Aug31-07, 12:48 AM
P: 9
Am I anywhere near correct?


1. The problem statement, all variables and given/known data
A ball is thrown and upward and reaches it's maximum height in 1.80 sec.

A. Find Initial Velocity
B. Find Max Height Reaced
C. Find Velocity 1.15 sec after being thrown.


2. Relevant equations



3. The attempt at a solution
A. .5(-9.8)*1.8^2= -15.87 m/sec
B. -15.87+.5(-9.8)*1.8^2 = 31.74m
C. .5(-9.8)1.15^2= -6.48 m/sec
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learningphysics
learningphysics is offline
#2
Aug31-07, 01:36 AM
HW Helper
P: 4,125
No, not near correct. For part a, you used a displacement formula... so the result won't be a velocity...

Hint: for part a) use the fact that v2 = v1 + at. You know v2, a and t... use those to calculate v1.

For part b) you made a mistake with the formula... it should be s = v1*t + 1/2 at^2... you didn't multiply v1 by t... and also the v1 is wrong since part a was wrong...

For part c)... here again you use a displacement formula... so the result that comes out will be displacement not a velocity... 1/2 at^2 is a distance not a velocity.


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