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February 28, 2015

February 28, 2015

Posted by **Hannah** on Wednesday, May 16, 2012 at 10:04pm.

My answer is at all times. Is this correct? Thank you.

- Physics(Please check) -
**Count Iblis**, Wednesday, May 16, 2012 at 10:17pmCorrect!

- Physics(Please check) -
**Hannah**, Wednesday, May 16, 2012 at 10:25pm1) How long does it take the ball to reach its highest point?

I am not sure what I would divide 24 by to find this.

2) How high above the starting point is the highest point?

I am not sure how to find this.

- Physics(Please check) -
**Count Iblis**, Wednesday, May 16, 2012 at 10:29pmWrite down the equation for the velocity as a function of time:

V(t) = V(0) - g t

where 9 = 9.81 m/s^2

Here we take the velocity positive if it is in the upward direction. When the ball is at the highest point, the velocity is zero. Clearly if the velocity is not zero, it is either going to move further upward, or if it is negative, it was at a higher point earlier.

- Physics(Please check) -
**Hannah**, Wednesday, May 16, 2012 at 10:41pmOk but where did the 9 come from?

- Physics(Please check) -
**Hannah**, Wednesday, May 16, 2012 at 10:44pmI know the highest point would be 29.4 but I do not know how to get this.

- Physics(Please check) -
**Elena**, Thursday, May 17, 2012 at 11:17amThere are two ways of solution

1. using kinematics.

v =vₒ - g•t,

Velocity at the highest point is zero, =>

0 = vₒ - g•t,

t =vₒ/g.

h = vₒ•t - g•t²/2 = vₒ²/2•g

2. using the law of conservation of energy

KE =PE

m•vₒ²/2 = m•g•h,

h = vₒ²/2•g.

h = (24)²/2•9.8 = 29.4 m

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