if a car moving 180km/h reduces to 72km, what is the percentage change in kinetic energy?

To calculate the percentage change in kinetic energy, we need to compare the initial kinetic energy (KEi) with the final kinetic energy (KEf) of the car.

The formula for kinetic energy is: KE = (1/2) * m * v^2, where m is the mass of the object and v is the velocity.

Let's assume we have a standard mass for the car, so we can ignore it for this calculation. Therefore, the equation becomes:

KE = (1/2) * v^2

Initially, the velocity of the car is 180 km/h, so we can convert it to m/s:
180 km/h = 180 * (1000 m/1 km) * (1 h/3600 s) = 50 m/s

Similarly, the final velocity of the car is 72 km/h, which can be converted to m/s:
72 km/h = 72 * (1000 m/1 km) * (1 h/3600 s) = 20 m/s

Now we can calculate the initial kinetic energy (KEi) and the final kinetic energy (KEf):

KEi = (1/2) * (50 m/s)^2 = 1250 J
KEf = (1/2) * (20 m/s)^2 = 200 J

Next, we can find the percentage change by using the formula:

Percentage change = ((KEf - KEi) / KEi) * 100

Substituting the values, we get:

Percentage change = ((200 J - 1250 J) / 1250 J) * 100 = (-1050 J / 1250 J) * 100 = -84%

So, the percentage change in kinetic energy is -84%. The negative sign represents a decrease in kinetic energy.