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Tension of string for a conical pendulum (10 points)?
A rock of mass 4.0 kg is tied to a string of length 1.7 m. The rock is held at rest as shown in the figure below so that the string is initially tight, and then it is released.
http://www.webassign.net/giocp1/6-p-049.gif
(b) What is the maximum tension in the string?
The answer is 46.5 N, I need help getting there, please explain. Thank you. Also, I calculated the speed of the rock when it reaches the lowest point to be 1.77 m/s, not sure if you'll need that, but there it is.
2 Answers
- odu83Lv 78 years agoFavorite Answer
The tension will be max at the lowest point of the swing
Using energy, the KE at that point will be
KE=.5*m*v^2=m*g*h
v^2=2*g*h
where h=1.7*(1-cos25)
and the centripetal force will be
m*v^2/r
or
m*2*g*(1-cos25)
the total tension will be
m*g*(1+2*(1-cos25))
46.5 is the answer
- 8 years ago
The formula is : T cos Ѳ = mg
Therefore, T= mg / cos Ѳ
Maximum value of T occurs when Ѳ is 0
because at the moment when the string is vertical, the weight acts maximum on the string
T = mg
= (4.0) (10)
= 40 N
Sorry, i don't understand why i didn't get the answer
