I pull back the string on a pendulum until it is at 60 degrees. I let go of it.

Question

I pull back the string on a pendulum until it is at 60 degrees. I let go of it. When the pendulum is at its minimum point (theta=0), what is its speed?

Possibly useful info: The string is 0.4 meters long.also m=0.05 km

Give your answer in units of meters per second, BUT DO NOT PUT THE UNITS IN YOUR ANSWER, JUST GIVE THE NUMBER THAT YOU GET IF YOU DO YOUR CALCULATION IN METERS PER SECOND!

part b
If I had asked you for the speed when it reaches theta=-30 degrees (i.e. it's on the left) what would your answer to the previous part be multiplied by?

Explanation / Answer

part a v=1.4 m/s part b mgr(1- cos60) = mgr(1- cos 30) + 0.5 mv^2 v= 1.19784 m/s v2/v1 = 0.856 so multiplication factor =0.856 part c see mgr(1- cos60) = 0.5 mv^2 can be written as: gr(1- cos60) = 0.5 v^2 so answer of the first part still remains unchanged as it is independent of mass so answer is no change

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