# Spinning Ball

A mass M of 2.47 kg is attached to the end of a string whose length is 0.410 m. The mass slides without friction on a horizontal surface as indicated in the diagram.

a)If the string can withstand a maximum tension of 113.1 N, what is the maximum tangential speed the ball can have before the cord breaks?
Answ: 4.33 m/s

b)The mass, with a new string, is whirled in a vertical circle of the same radius about a fixed point. Find the magnitude of the tension when the mass is at the top if its speed at the top is 6.69 m/s.
Answ: 2.45×102 N

For part a) i used the formulaa 1) F=ma 2)a=rw^2 3) V=rw to get the right answer but for part b) I used 1)V=rw 2) a=rw^2 3)T=ma but im not getting the right answer. Am I doing something wrong?

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BJ

Päällikkö
Homework Helper
b) the motion is vertical, so you must take gravity into account.

siddharth
Homework Helper
Gold Member
In the second case, gravity is also acting.
So, mv^2/r=mg+T.

T = m ((v^2/r)-g)