Tension in vine at lowest point and pendulum potential energy change

[bhipps]

OMG these 2 problems are driving me insane! If you are able to help, please show steps so I can gain a good understanding...

1.) Jeff of the Jungle swings on a 7.6- vine that initially makes an angle of 32 with the vertical. If Jeff starts at rest and has a mass of 73 , what is the tension in the vine at the lowest point of the swing?

* I do know that the tension on the vine at rest is m(g) at rest...how am I supposed to incorporate theta?


2.) A 0.43 pendulum bob is attached to a string 1.2 long, making an angle of 35 with the vertical. What is the change in the gravitational potential energy of the system as the bob swings from point A to point B (from right to left)?

 

[cragar]

on the second one you could find the change in height and use. U=mgh
U= gravitational potential energy
And also on the first one you could find the change in height and use mgh and then equal this to kinetic energy to get a velocity and then use the centripetal force. This should work but I am also really tired right now.

 

[sophiecentaur]

As cragar says - just calculate the change in gpe and this will tell you the KE increase, which will give you the force involved.

It's interesting to note that, on a swing of any length, if you are released with the string horizontal, you will always pull 3g at the bottom. It's just that, on a long swing, the experience lasts longer.