# Homework Help: Brakes on a car-Energy related question

1. Jun 5, 2013

### alingy1

In terms of energy, why does a car going fast absolutely needs good brakes? What are the main physical constraints to optimize?

Friction should be increased. But, that's what I pretty much I have to say. What else could be said? I've been racking my brains for two hours picturing a car in my head. Nothing comes to my mind!

2. Jun 5, 2013

### SteamKing

Staff Emeritus
Would you ride in a fast car with dodgy brakes?

3. Jun 6, 2013

### rcgldr

The friction in the brakes needs to be sufficiently greater than the maximum static friction between the tires and pavement. The brakes need to be able to dissipate the heat energy produced from braking so they do not fade. The worst case scenario for heat dissipation for a street car would be going down long steep hill. For a race car, it's the repeated amount of maximum braking.

4. Jun 6, 2013

### CWatters

What rcgldr said.

The brakes need to be able to dissipate all the Kenetic Energy of the car in the form of heat.

Presumably you know the equation for the KE of the car so ask yourself this question:

Which would give the brakes more work to do..

a) doubling the mass of the car or
b) doubling the velocity of the car?