# Halp with physics? (in Off-topic)

## AdmanteNovember 29 2009 3:46 PM EST

I'm not asking for an answer to this problem since I think I've already gotten one. I would like to confirm my process though.

A pendulum is 0.800m long and the bob has a mass of 1.00 kg. When the string makes an angle of (theta) = 15.0 degrees with the vertical, the bob is moving at 1.40 m/s. Find the tangential and radial acceleration components and the tension in the string.

From what I've read online, radial acceleration is always equal to v^2/r, which in this case would be (1.40m/s)^2/0.800 m = 2.45 m/s^2.

Tangential acceleration would be solved using Newton's Second Law. With the tangential axis being x, and radial axis being y, only the x component of weight is causing tangential motion of the bob. So F=ma => mg sin theta = m*acceleration tangential => acceleration tangential = 1.00 kg*9.8 m/s^2*sin (15.0 degrees) / 1.00 kg = 2.54 m/s^2.

This seems too straightforward to be right... Am I missing something?

## SickoneNovember 29 2009 4:35 PM EST

You're not missing anything.
ar = v^2/r, at = g*sin(angle)
Physics is pretty simple ;)

## SickoneNovember 29 2009 4:37 PM EST

P.S. Unless the mass is needed in another calculation in the same problem, the mass of the pendulum is completely irrelevant.
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