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• #### Whch formula is the 'right formula'... PLS HELP 1loveB00ks

2012 Q12b

I'm having a little trouble with this question. Any help at all would be greatly appreciated.

I used the formula w2 = force / radius x mass thinking that if i sub the values in, this would be sufficient enough tho answer the question. The marking scheme however uses the formula T = 2pi/ w. Why use a formula that is for simple harmonic motion ? The question states that the person is swinging a mass. Would this not be centripetal force and not harmonic motion ? Is there a reason why using the centripetal formula doesn't give the correct answer ?

Pls help ?

1. #### acc98

hi, might be a little late but anyways....

ive done the question and the first thing i did was draw a diagram and then look at the formulas for circular motion and SHM

, i used the formula W=theta (any angle)/ time, because we have that it goes one revolution ( one circle = 2 pie radians) in 0.8 seconds.

W= 2pie/ 0.8 = 7.85radians per second.

in the marking scheme they used T(time taken to complete one cycle, period)=2pie/W

rearranged.... W= 2pie/T

T= 0.8s

idk why the SHM formulas work and the centripital force formulas dont but i generally just go with the formulas that i have the info for. how did you get the force for the F=mrW(squared) formula?