1. Aug 19, 2008

### mkha0246

1. The problem statement, all variables and given/known data
A person places a 2.2kg truck against a horizontal spring (k=2300N/m) on a frictionless horizontal surface. The spring is compressed 15cm and released.

a) How much energy is stored in the spring just before the truck is released?

b) What is the velocity of the truck after it is "launched" (leaves the spring)?

c) If the spring inadvertently becomes hooked to the the bumper of the truck, what will be the period of the truck's oscillation?

d) As in part c, if the spring becomes hooked to the back of the truck calculate the location of the truck 0.31 seconds after the truck is released?
2. Relevant equations

3. The attempt at a solution
i tried to use the pe=1/2kx^2 equation for the first part but im forgetting what is k is again. Also my weakness is in oscillation questions because after 3 months of summer vacation im forgetting if we would use KE=1/2mv^2. Im utterly confused with thi problem.

Last edited: Aug 19, 2008
2. Aug 19, 2008

### Redbelly98

Staff Emeritus
(a) k is the spring constant. Use the value given at the beginning of your message.

(b) Yes, use KE = 1/2 m v^2

Hope that helps get things started.

3. Aug 19, 2008

### Jwill

k is the spring coefficient stated in the problem. The larger the coefficient the larger the potential energy.
Yes, and something to remember is PE + KE = ME.

4. Aug 21, 2008

### mkha0246

so for part a you would use PE=1/2kx^2 and input k with 2300N/m and x with the displacement of 15cm?
and for part b would PE=KE so to find v because if PE doesnt equal KE then there will be two variables in the KE=1/2mv^2 equation and then you wont be able to find velocity.
also thanks for everyone's advice in this!!!

5. Aug 21, 2008

### Redbelly98

Staff Emeritus
Yes. Just be careful with the units.

That's sort of right. You'll get the right answer to this problem, but I'm not sure you quite understand why saying KE = PE works here, whereas that relation is not always true in general.

To understand it, your book probably has an equation expression conservation of total energy (KE+PE), along with some mention of "initial and final", "before and after", "1 and 2" or something like that. (Different texts will word it differently.)

Regards,

Mark