Oscillation Problem Please HELP need for school

[mkha0246]

Homework Statement

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?

Homework Equations

The Attempt at a Solution

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

 

[Redbelly98]

(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.

 

[Jwill]

i tried to use the pe=1/2kx^2 equation for the first part but I am forgetting what is k is again.

k is the spring coefficient stated in the problem. The larger the coefficient the larger the potential energy.

Also my weakness is in oscillation questions because after 3 months of summer vacation I am forgetting if we would use KE=1/2mv^2. I am utterly confused with thi problem.

Yes, and something to remember is PE + KE = ME.

 

[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 doesn't equal KE then there will be two variables in the KE=1/2mv^2 equation and then you won't be able to find velocity.
also thanks for everyone's advice in this!

 

[Redbelly98]

so for part a you would use PE=1/2kx^2 and input k with 2300N/m and x with the displacement of 15cm?

Yes. Just be careful with the units.

... and for part b would PE=KE so to find v because if PE doesn't equal KE then there will be two variables in the KE=1/2mv^2 equation and then you won't be able to find velocity.
also thanks for everyone's advice in this!

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