Initially a body moves in one direction and has kinetic energy K.Then it moves in the opposite direction with three times its initial speed.What is the kinetic energy now?
A)K
B)3K
C)-3K
D)9K
E)-9K

Question

Quizplus · Accepted Answer

Kinetic energy is proportional to the velocity squared. When the body moves in the opposite direction with three times its initial speed, its velocity becomes -3v (where v is the initial velocity). Therefore, the kinetic energy becomes (1/2)mv^2 * 9 = 9K.

Initially a Body Moves in One Direction and Has Kinetic