(adsbygoogle = window.adsbygoogle || []).push({}); Question:

A frictionless block of mass 2.35 kg is attached to an ideal spring with force constant 310 N/m. At t=0 the spring is neither stretched nor compressed and the block is moving in the negative direction at a speed of 12.6 m/s.

1.Find the amplitude.

I got this without a problem. I used the formula A = square root of [tex]x_i^2[/tex] + [tex]v_i^2[/tex]/[tex]\omega^2[/tex]. [tex]\omega = \sqrt{k/m} = 11.49[/tex] rad/s. Plugging in known values results in 1.10 m, which is correct.

2.Find the phase angle.

Here's where I don't know why my answer is not correct.

I use the equation [tex]v_i = -\omega * A * sin(\omega*t + \phi)[/tex]. I know the initial velocity, I know the angular frequency, and I know the amplitude. I'm solving for the angle in radians.

[tex]-12.6 = -(11.49)(1.10)(sin(\phi)[/tex] This is at time t, so [tex]\omega * t[/tex] = 0.

I get [tex]\phi = 85.5 ^\circ[/tex]. Converting it into radians, it's 1.49 (rad).

This isn't right, though.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Finding the phase angle in simple harmonic motion

**Physics Forums | Science Articles, Homework Help, Discussion**