# Ball thrown up with an initial speed of 27.0 m/s

1. Oct 21, 2008

### evan b

1. The problem statement, all variables and given/known data
A) The ball's PE is a constant.
B) The velocity vector and the acceleration vector are in the same direction after t= 7.3s.
C) The acceleration is constant.
D) The acceleration is 0 near t= 7.3s.
E) Maximum height is reached at about t=7.3s.
F) The ball's KE increases during the first second.

3. The attempt at a solution
I am pretty sure of the following. Somewhere i am wrong.
A is false
B is true (given once it hits 7.3, gravity is negative(acceleration) and the direction is necative
C is true because accel is gravity and that is always constant.
D is false because if the gravity is constant than it wouldnt be zero
E is true because it starts coming down after 7.3 s
F is true because KE is zero when the ball is in hand but when he releases it, it gains

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2. Oct 21, 2008

### Rake-MC

I can't see the image until it's approved, but this is my input

A - I would agree that this is false.
B - mathematically I would agree, however I would say that the ball has long since hit the ground at this point. (possibly numbers are wrong)
C - I would agree that this is true.
D - I agree that this is false.
E - I would disagree here, how did you come to this conclusion? It looks more like 2.75 seconds to me. Unless you've stated some of the numbers wrong/I've misinterpreted them.
F - kinetic energy of course being: .5mv^2 Think about which way the ball is accelerating, think of if v is increasing or decreasing.

EDIT: latex isn't working for me