# Energy/Work Questions?

1. Feb 17, 2015

1. The problem statement, all variables and given/known data
An elastic powered slingshot can launch a 100 g marble into the air 18 m by using elastics.
a) W hat is the average force exerted by the elastic if the elastics stretches 65.0 cm before it launches the
marble?
b) How fast is the marble going straight up when it is 10 m above the ground?
c) W hat speed does the marble leave the sling shot?
d) How high is the marble from the ground when it is moving at 10 m/s?

Thanks!

2. Relevant equations

3. The attempt at a solution
So i know W=Eg=mgh, but what height would i put for h? 18m or 65 cm?

2. Feb 17, 2015

### Staff: Mentor

Welcome to the PF.

a) What is the equation for Work as a function of Force and Distance? Given your W=mgh equation, what is the energy that the marble has when it leaves the launcher?

b) What is the equation for Total Energy in terms of Potential Energy and Kinetic Energy?

c) (combine a & b...)

d) (similar to b)

3. Feb 17, 2015

### lightgrav

which height has gravity being the only Force applied?
. . . how do you compute Work from Force?

4. Feb 17, 2015

so (.1)(9.8) (.65) should give me energy/work which i can then rearrange to find force?

5. Feb 17, 2015

### Staff: Mentor

Not quite. What equation are you trying to use there? What are the units of each quantity? It's a good idea to get in the habit of first writing the equation symbolically and then writing it with numbers and units for each symbol, and then etc....

6. Feb 19, 2015