Homework Help: Physics

Posted by Tanysha on Tuesday, October 11, 2011 at 11:10am.

In running the 40 m dash in tryouts fot the Notre Dame football team, Zach S. completes the 40 m in 4.8 seconds. Assuming constant acceleration throughout the run, find his velocity at the end of 40 m and his acceleration during the 40 m.

Physics - drwls, Tuesday, October 11, 2011 at 11:59am
For the acceleration a, solve
X = (1/2) a t^2

a = 2X/t^2 = 3.472 m/s^2

For the velocity after 4.8 seconds, solve
V = a t

You will get a number that is higher than the world record average speed for the 100 m dash. I do not believe the figures. The problem is probably the assumption that constant acceleration can be maintained for 40 meters.
Physics - Steve, Tuesday, October 11, 2011 at 12:00pm
You know, if you have a problem with time, acceleration, velocity and distance, before bothering to post the question, try using the formulas you know and love:

v = at
s = 1/2 at^2

Since there is constant acceleration,

s = 1/2 at^2
40 = 1/2 a * 4.8^2
a = 3.47222 m/s^2

v = at = 3.47222 * 4.8 = 16.67 m/s

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