# Physics to drwls question to answer given earlier

posted by
**Angelina** on
.

A 0.700-kg ball is on the end of a rope that is 0.90 m in length. The ball and rope are attached to a pole and the entire apparatus, including the pole, rotates about the pole's symmetry axis. The rope makes an angle of 70.0° with respect to the vertical as shown. What is the tangential speed of the ball?

physics - Angelina, Friday, February 17, 2012 at 12:00am

I was thinking that it would be .90tan(70)=2.47 m/s^2 but I am wrong so I don't know how to do this...

physics - drwls, Friday, February 17, 2012 at 2:28am

Let the rope tension be T.

T sin70 = M V^2/R

T cos70 = M g

Now, divide the first equation by the second one.

tan70 = V^2/(R*g)

V^2 = (0.90)(9.8)(2.747)= 24.23 m^2/s^2

V = 4.92 m/s

Your answer does not have the dimensions of velocity, and must depend upon g.

physics - Angelina, Friday, February 17, 2012 at 4:34pm

What is the tangential speed of the ball?

thnks but i tried both 24.23m^2/s^2 and 4.92 n neither are right i don't understand whats wrong