A 1200kg car going 25m/s is brought to a stop using its brakes. Assuming that a total of approximately 20kg of iron in the brakes and wheels absorbs the heat produced by friction.

What was the car’s original kinetic energy and after the car has stopped, what is the change in temperature of the brakes and wheels?

To find the original kinetic energy of the car, we can use the formula:

Kinetic Energy (KE) = 0.5 * mass * velocity^2

Given that the mass of the car is 1200kg and the velocity is 25m/s, we can calculate the original kinetic energy:

KE = 0.5 * 1200kg * (25m/s)^2
KE = 0.5 * 1200kg * 625m^2/s^2
KE = 375,000 Joules

Therefore, the car's original kinetic energy is 375,000 Joules.

To find the change in temperature of the brakes and wheels, we need to calculate the amount of heat produced by friction. We know that approximately 20kg of iron absorbs this heat.

The heat produced by friction can be calculated using the formula:

Heat = mass * specific heat capacity * temperature change

The specific heat capacity of iron is 450 J/kg°C. Let's assume the car comes to a stop, so its final velocity is 0 m/s. The change in kinetic energy is equal to the heat produced by friction.

Change in Kinetic Energy (ΔKE) = Heat = mass * specific heat capacity * temperature change

Since the final kinetic energy is zero, the change in kinetic energy from the initial value (375,000J) to zero is -375,000J.

-375,000J = 20kg * 450J/kg°C * temperature change

To calculate the change in temperature, we rearrange the equation:

temperature change = (-375,000J) / (20kg * 450J/kg°C)
temperature change = -41.67°C

Therefore, the change in temperature of the brakes and wheels is approximately -41.67°C.

Iniital KE=1/2 m v^2

heat in the stopping process: Initial KE

massiron*specificheatiron*(deltaTemp)=heat

solve for deltatemp