# Mass oscillating on spring

## Homework Statement

The position of a mass that is oscillating on a spring is given by x(t) = (14.5cm)cos[(14.0s-1)t].
What is the speed of the mass when t = 0.820 s?

## Homework Equations

A= Amplitude
W= Angular frequency

x(t) = ACos(Wt)
v(t) = -WASin(Wt)

## The Attempt at a Solution

v(0.820) = (-14.0)(14.5)Sin[(14.0)(0.820)]
= (-203)Sin[11.48]
= -40.4 cm/s

This seems so easy and yet apparently I have the wrong answer... any insight? :/ Thanks in advance

Related Introductory Physics Homework Help News on Phys.org
fluidistic
Gold Member
What you did seems right to me.

Check the units of your frequency. It looks like you have the value in Hertz (or oscillations per second); try converting the instances of frequency to radians per second (and if you're carrying out the sine calculation on a calculator then change the mode to radians instead of degrees).

Check the units of your frequency. It looks like you have the value in Hertz (or oscillations per second); try converting the instances of frequency to radians per second (and if you're carrying out the sine calculation on a calculator then change the mode to radians instead of degrees).
Okay, that makes more sense...

W=2 x pi x freq

thus v(t) = -(2 pi 14)(14.5)Sin[(2 pi 14)(0.82)]

which gives -160 cm/s (with 3 sig figs)... but it still isn't right.
I suppose there shouldn't be a negative should there? Since speed is scalar... but 160 isn't the right answer either. :/