- #1

stanton

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## Homework Statement

A slingshot consists of a light leather cup, containing a stone, that is pulled back against two parallel rubber bands. It takes a force of 15 N to stretch either one of these bands 1.0 cm.

(a) What is the potential energy stored in the two bands together when a 50-g stone is placed in the cup and pulled back 0.20 m from the equilibrium position?

(b) With what speed does the stone leave the slingshot?

The answers are a) PE =

**60 J**b) v =

**49 m/s**

## Homework Equations

F=kx PE=1/2kx^2

## The Attempt at a Solution

a)

F=kx

15 = k(0.01) → k=1500 N/m

PE = 1/2 k x^2

= 1/2 (1500)(.20)2

=

**30 J**

b)

PE1=KE1, KE = 1/2mv^2

1/2mv^2 = 30

1/2(0.050)v^2 = 30;

v=

**34.6 m/s**

Any comment or help would be appreciated about why I got the answers wrong. Thank you.