Calculating Work Done by Gravity on Thrown Ball

[BuBbLeS01]

Homework Statement

A 0.113-kg ball is thrown straight up from 2.07 m above the ground. It's initial vertical speed is 7.6 m/s. A short time later, it hits the ground. Calculate the total work done by the force of gravity during that time.

Homework Equations

The Attempt at a Solution

can I use...
1/2mv^2 = mgh
1/2v^2 - gh = W

 

[G01]

Think of the problem like this:

What is the initial energy of the ball? (When it is thrown)

What is the final energy of the ball? (When it lands)

If you know those two quantities, you should be able to find the work.

 

[Vijay Bhatnagar]

Work done = Force x Displacement. What is gravitational force acting on the ball? What is the displacement (not distance travelled) between the initial position and final positions of the ball?

 

[BuBbLeS01]

W=Fd
gravitational force = g
displacement = 2.07m

 

[BuBbLeS01]

Okay so I am not understanding this problem. Apparently from 2.07m and above there is no work done but I don't know why?? And I get...
W = Fd
Ug = mgh
K = 1/2mv^2
Wtot = mgh = 2.29J

I was trying to do W = Change in K + change in Ug...why is this not the case?

 

[hotcommodity]

The total work done on the ball is given by the ball's overall change in kinetic energy. When the ball goes up from its initial height, and reaches the top of its path, its kinetic energy has decreased. When it comes down from the top and back to that same initial height, its kinetic energy has increased. The decrease and increase in kinetic energy will add to zero, because we're ignoring air resistance. You want to find the change in the ball's kineteic energy from 2.07m to the ground. Does that help?

 

[BuBbLeS01]

Oh okay...thank you that makes sense!