# HW problemos

ACLerok
I'm having trouble with one problem. The question aske me to finf the amount of power from the equation I found for work. Here is the equation for work: W=F*v*t*cos(theta) I am supposed to come up with an equation that will tell me how much power this is using the variables in the equation. A friend told me to take the derivative but I'm nto sure how to. How do i go about this?

Oh and this as well:
To stretch a spring a distance x_1 from its unstretched length, an amount of work of W must be done.

How much work must be done to compress this spring a distance x_2 from its unstretched length?

## Answers and Replies

lastlaugh
power is work/time
that should be a pretty good hint

Homework Helper
Knowing the definition of "power" would be extremely useful in doing any problem about power! Are you sure that you do?

Oh and this as well:
To stretch a spring a distance x_1 from its unstretched length, an amount of work of W must be done.

How much work must be done to compress this spring a distance x_2 from its unstretched length?

You need to know either:
that the formula for work done in either compressing or stretching a spring a distance x is (1/2)kx2 where k is the spring constant and x is the distance stretched or compressed or
(what follows immediately from that formula)
that the work done in compressing or stretching a spring a distance x is proportional to x2.

IF W is the work done stretching the spring a distance x_1 and W_2 is the work done in compressing it a distance x_2, then
W/(x_1)2= W_2/(x_2)2(= (1/2)k) so that

W_2= (x_2/x_1)2 W_1