A mass of 100 g is tied to the end of an 80.0-cm string and swings in a vertical circle about a fixed center under the influence of gravity. The speed of the mass at the top of the swing is 3.50 m/s. What is the speed of the mass at the bottom of its swing?

the speed of the mass at the bottom of its swing is 6.61m/s

Explanation:

Applying energy conservation

There is no potential energy at the bottom as the body will have a kinetic energy there.

h= 2R = 1.6m as the diameter of the circle will represent the height in the circle.

g = 9.8m/s^2

m will cancel out, so the net equation becomes.

                 =

                  =  15.68+ 6.125

              =  21.805

(Vb)^2 = 2*21.805

     = 43.64

Vb = 6.61m/s

b would be the answer

your answer is c! hope this : )