# Acceleration Deceleration Physics Problem

1. Sep 1, 2009

### spaceshipone

A car has a maximum constant acceleration of 10 ft/s^2 and a maximum constant deceleration of 15 ft/s^2. determine the minimum amount of time it would take to drive one mile assuming the car starts and ends at rest and never exceeds the speed limit 55 mi/hr.

Why do you need to know the deceleration constant if we are talking about the car accelerating and going to 55 mi/hr?
I would assume you just plug it into the constant acceleration formula and that is it.
I was also thinking maybe it has to accelerate to first at a constant rate and then decelerate to slow to 55 mph. I which case I have no idea how to solve the problem.

Anyone wanna take a stab at this?

2. Sep 1, 2009

### rl.bhat

Imagine you are driving from place A to place B. What do you do?
You start from rest, then accelerate until you reach the speed limit. You drive some time, then when you are near B, you apply the brakes to stop the car at B. Total distance is 1 mile.
Find t and S during acceleration and retardation, using appropriate kinematic equation.
Find the remaining distance which covered with uniform velocity. From that find the time taken to cover that distance. So you can find the total time to cover the whole distance.