Dynamics, Forces Explanation

[gunterZA]

Hi,

I am doing a review for a Dynamics exam, but I am having trouble with this one question (below).

Please note the top of the picture contains the answers.

What I have done is make a free body diagram that includes the tension of the cable and the weight of the rider/swing. So according to my calculations for part i:

T= mg cos (30) = 680N

The tangential acceleration is 0

Which according to the provided solutions is incorrect. Am I missing a force?

I figured the tension is integral to finding the velocity of the rider. So I want to get my tension right before I proceed with finding the velocity, though I am also having trouble figuring out how to relate tension and velocity of the acceleration of the rider is 0

I would appreciate an explanation so I can understand.

 

[OceanBreeze]

Try using Tan Θ to get Fn. Once you have that you should have no trouble calculating tension.

The tangential acceleration is 0, but there is another kind of acceleration!

To get Vt, just remember that centripetal force (Fn) equals mass x centripetal acceleration, and centripetal acceleration equals Vt^2 / r.

You should be able to work it out now, especially since you already have the correct answers to compare with.