# Homework Help: Energy of a system

1. Dec 27, 2017

### Fatima Hasan

1. The problem statement, all variables and given/known data
A basketball with a mass of 0.56 kg drops from a height of 5 m and bounces off the floor back up to a maximum height of 4.3 m .Find the work done on the ball by the ground during the time the ball is in contact with it.

2. Relevant equations
W = - Δ Ug
Ug = mgh
3. The attempt at a solution
ΔUg = mghƒ - mghι
= 0.56*10*4.3 - 0.56*10*5 = - 3.92 J
W= - Ug = 3.92 J

2. Dec 27, 2017

### PhanthomJay

The magnitude of the work done by the ground is correct, however you have a signage error because you incorrectly applied the equation for work done by the ground. The formula you used is for the work done by gravity. What equation should you be using for work done by the ground, which is work done by a non conservative force?

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