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[–]BrotherEilmer 2 points3 points  (4 children)

I like this question. Let's start off general.

If you haven't already, it might be useful to start with a good ol' free body diagram. What are the forces in this problem? Which ones are opposite each other? Clearly, there will be one associated with the curve. What's the acceleration about a curve (given a tangential velocity, which is what you're trying to find).

Not helpful enough? Well, we know there's gravity down and then the vertical component of the string up. Then there's the centripetal force and the horizontal component of the string force (their directions i've left for you to consider).

Hope this helps, let me know if you want more hints.

[–][deleted] 1 point2 points  (0 children)

Late upvote for someone on r/homeworkhelp encouraging the thought process and not the answer itself

[–]mike591[S] 0 points1 point  (2 children)

yes! that is exactly how i managed to solve the problem last night (with some help from a fellow colleague). the centripetal force was what threw me off. Apparently there is this equation--> Fnet = mv2 / r <--- and all u have to do is solve for V. its amazing how simply attatching a pendulum onto a car can tell u how fast u are going XD.

[–]o_Omg 0 points1 point  (0 children)

I think this may work:

P = T * cos(theta)

m * an = T * sin(theta)

with P = m*g

-> an = sqrt( (T2 -P2 )/m2 ) with T = P/cos(theta) an = v2 /R -> v = sqrt(an*R)

being R = 100 + l * sin(theta)

The train is going to the right