# Physics question (elasticity)

• 12-14-2003
Leeman_s
Physics question (elasticity)
What is the elasticity of a ball which hits a wall at 10 m/s and rebounds off the wall at 8 m/s? (answer to 2 significant digits)

That's an online question for school. All of us trying to do it can't get it. It should be 80% I think, but it's not. And it's not a multiple choice question.

Anyone know how you would do that?
• 12-14-2003
Govtcheez
5.
• 12-14-2003
Leeman_s
What....? 5 is the answer? Huh? I can't make sense out of that...and it should be a two digit number (yes I know how sig figs work but I know that what my teacher implies by that)
• 12-14-2003
ZerOrDie
64%
• 12-14-2003
XSquared
8.0x10^-1
• 12-14-2003
XSquared
Quote:

Originally posted by ZerOrDie
64%
How'd you get that?
• 12-14-2003
Thantos
3X

Now just have to solve for X. :D
• 12-14-2003
Xei
e = ( 1 - ((EKInitial - EKFinal) / EKInitial)) *100 = x%

We will substitute any mass. Lets say 1kg.

EK = (1/2)mv^2

EKInitial = (1/2)(1)(10)^2 = 50J
EKFinal = (1/2)(1)(8^2) = 32J

((50 - 32) / 50) * 100 = 36%

1 - .36 = .64
.64 * 100 = 64%

The ball has an elasticity of 64% (as 36% of the Kinetic energy was lost). Just remember your conservation of energy.
• 12-14-2003
ZerOrDie
:D looks like someone took the time to explain my answer lol
• 12-14-2003
Xei
Quote:

Originally posted by ZerOrDie
:D looks like someone took the time to explain my answer lol
Yes. I had to look back on some previous work because I realized that I actually forgot how to calculate the elasticity of an object - which frusterated me to no end.
• 12-15-2003
Leeman_s
im so mad. I even tried that, but it said it was incorrect so I reverted to 80%! I think it has problems with how you enter the answer, like it'd make a difference if it was 64, 64%, or 64 %

That threw me off then, indeed!
• 12-15-2003
Xei
Try .64