find the kinetic energy in ergs

Question

A point-mass of 15 grams at the end of a massless 20 centimeter long string is rotated at a rate of 3 revolutions per second. Find the kinetic energy (ergs) of the point mass.

Answer 1

Hello Lily

A point-mass of 15 grams at the end of a massless 20 centimeter long string is rotated at a rate of 3 revolutions per second. Find the kinetic energy (ergs) of the point mass.

m = 15*10^-3 Kg , r= 0.2 m

KE of Rotation = 1/2 I w² where I = m r² and w= 2*pi * frequency

I = 15*10^-3 (0.2)² Kgm² = 6*10^-4 Kgm²

KE = 0.106 J

Now change J to erg using 1 J = 10⁷ erg = 1.1 * 10⁶ erg