Bottom of a pendulum, what is tension

[mikefitz]

A pendulum is 0.7 m long and the bob has a mass of 1.0 kg. At the bottom of its swing, the bob's speed is 1.6 m/s. What is the tension in the string at the bottom of the swing?

I know that I can use centripetal force, which can be calculated from v -

ma(c) = (mv^2)/r

I get 3.6571 N as my answer, why is this wrong? thanks

 

[radou]

The tension equals T = mv^2/r + mg.

 

[mikefitz]

T= 1(1.6^2)/.7 + 1(9.81) = 13.47 N

This is still incorrect... any other clues? thanks

 

[skeeter]

what makes you think it's incorrect? ... cause it is correct.

at the bottom of the swing, Fnet = T - mg

mv^2/r = T - mg

T = mv^2/r + mg