A very small 100-g object is attached to one end of a massless 10-cm rod that is pivoted without friction about the opposite end. The rod is held vertical, with the object at the top, and released, allowing the rod to swing. What is the speed of the object at the instant that the rod is horizontal?
A) 0.71 m/s
B) 4.0 m/s
C) 1.4 m/s
D) 2.8 m/s
E) 2.8 m/s

Question

A very small 100-g object is attached to one end of a massless 10-cm rod that is pivoted without friction about the opposite end. The rod is held vertical, with the object at the top, and released, allowing the rod to swing. What is the speed of the object at the instant that the rod is horizontal?
A) 0.71 m/s
B) 4.0 m/s
C) 1.4 m/s
D) 2.8 m/s
E) 2.8  m/s

Quizplus · Accepted Answer

The potential energy at the top is converted to kinetic energy at the horizontal position. Using conservation of energy: mgh = 0.5mv^2, where h = 0.1 m. Solving gives v = sqrt(2gh) = sqrt(2*9.8*0.1) = 1.4 m/s.

A Very Small 100-G Object Is Attached to One End