# Homework Help: Car Braking

1. Jan 25, 2009

### NYCHE89

1. The problem statement, all variables and given/known data

How much pressure must be exerted by the braking system of a car weighing 3000 lb, if you want to stop it from 40 mph to 0 in 1.5 seconds? Assume the total braking surface of the four wheels is 96 in^2. How much force must be exerted by your foot on the brake pedal in the absence of a vacuum assist, if the brake cylinder diameter is 3/4 inch?

2. Relevant equations

Am I supposed to know something about cars to answer this? I don't understand how to even start this problem.

3. The attempt at a solution

2. Jan 25, 2009

### mgb_phys

What equation link force, mass and accelration?
What do you know about the ratio of cylinders in hyraulics?

3. Jan 25, 2009

### NYCHE89

so I can use F=ma and V= V_initial + a*t by rearranging and coming up with
F=(m*Delta V)/t ?

As to your second question, I haven't learned anything about the ratio of cylinders or hydraulics. What is the ratio?

4. Jan 25, 2009