Question

A small mass attached to a string rotates on frictionless table top as
shown. If the tension in the string is increased by pulling the string
causing the radius of the circular motion to decrease by a factor of 2,
the kinetic energy of the mass will
(a) remain constant
(b) increase by a factor of 2
(c) increase by a factor of 4
(d) decrease by a factor of 2

Answer 1

Answer:

option c

K.E. = L22I From angular momentum conservation about centre. L → constant I = mr2 K.E.' = L22 (mr'2)r' = r2 K.E.' = 4 K.E. K.E. is increased by a factor of 4.

Answer 2

Answer:

A small mass attached to a string rotates on frictionless table top as

shown. If the tension in the string is increased by pulling the string

causing the radius of the circular motion to decrease by a factor of 2,

the kinetic energy of the mass will

(a) remain constant

(b) increase by a factor of 2

(c) increase by a factor of 4 ✔️✔️

(d) decrease by a factor of 2