# Velocity/acceleration/time to stop

• lauriecherie
In summary, the conversation discusses the calculation of the minimum time required to slow down a car from 132 km/h to 90 km/h using the brake's capability of 4.9 m/s^2. The equations v(t)= at + initial velocity and (final velocity^2) - (initial velocity^2) = 2*a*delta X (change in position) are used to find the solution. A calculation error is identified and corrected, resulting in a final answer of 2.380952388 seconds.
lauriecherie

## Homework Statement

The brakes on your car are capable of slowing down your car at a rate of 4.9 m/s^2.
If you are going 132 km/h and suddenly see a state trooper, what is the minimum time in which you can get your car under the 90 km/h speed limit?

## Homework Equations

v(t)= at + initial velocity

(final velocity^2) - (initial velocity^2) = 2*a*delta X (change in position)

## The Attempt at a Solution

I came out with 8.57 seconds. Is there some converting I maybe missed?

Hi Laurie, welcome to PF!
I don't know how you got 8.57. I got between 2 and 3s. Show your calc and we'll find your error.
Did you remember to convert the speeds to m/s ?

Delphi51 said:
Hi Laurie, welcome to PF!
I don't know how you got 8.57. I got between 2 and 3s. Show your calc and we'll find your error.
Did you remember to convert the speeds to m/s ?

No, I didn't convert. Whoops. So let me work this out again. Thanks for the advice.

2.380952388 seconds. :!) Thanks soooo much for your help!

Most welcome!

## 1. What is velocity?

Velocity is a measure of how fast an object is moving in a particular direction. It is a vector quantity, meaning it has both magnitude (speed) and direction.

## 2. How is velocity calculated?

Velocity is calculated by dividing the change in an object's position (displacement) by the time it took for that change to occur. The formula for velocity is v = Δx/Δt, where v is velocity, Δx is change in position, and Δt is change in time.

## 3. What is acceleration?

Acceleration is a measure of how quickly an object's velocity is changing. It is a vector quantity, meaning it has both magnitude and direction. Acceleration can be caused by a change in speed, direction, or both.

## 4. How is acceleration related to velocity?

Acceleration is the rate of change of velocity. This means that if an object's velocity is changing, it is accelerating. The direction of acceleration is in the same direction as the change in velocity.

## 5. How long does it take for an object to stop?

The time it takes for an object to stop depends on its initial velocity and the acceleration acting on it. The formula for calculating the time it takes for an object to stop is t = v/a, where t is time, v is initial velocity, and a is acceleration. This assumes that the object is decelerating at a constant rate.

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