# A car moves along a level road. If the car's velocity changes from 60 mph due east to 60 mph due...

## Question:

A car moves along a level road. If the car's velocity changes from 60 mph due east to 60 mph due west, the kinetic energy of the car does which of the following? (Assume the car makes a U-turn.)

a) decreases

b) first increases, then decreases

c) increases

d) remains the same

e) first decreases, then increases

## Kinetic Energy:

Kinetic Energy is the energy being carried by an object due to its motion. The total kinetic energy of an object consists of its linear and angular kinetic energy. The linear kinetic energy of an object is due to its translation while its angular kinetic energy is due to its rotation. The linear kinetic energy can be determined using the object's mass and velocity while the angular kinetic energy can be determined using its rotational inertial and angular velocity.

## Answer and Explanation:

The kinetic energy of the car moving along a level road is given by,

{eq}KE = \frac {1}{2} mv^2 {/eq} where

{eq}KE {/eq} is the magnitude of the car's kinetic energy

{eq}m {/eq} is the mass of the car

{eq}v {/eq} is the car's velocity

From this formula, it can be deduced that in order to make a u-turn the car has to decelerate even as far as coming to a rest before accelerating to the given speed due west. Hence, the kinetic energy must first be decreased then increase. The answer therefore is E.

{eq}\boxed {E} {/eq}