# What's the deceleration of the car?

In summary, to cross the first pressure-activated strip at the speed of 19.6 meters per second, the car must decelerate by at least 0.5 meters per second.

## Homework Statement

A speed trap is set up with two pressure activated strips placed across a highway, 128 meters apart. A car is speeding along at 28.8 meters per second, while the speed limit is only 19.6 meters per second. At the instant the car activates the first strip, the driver begins slowing down. What minimum deceleration (magnitude only) is needed so that the driver's average speed is within the limit by the time the car crosses the second strip?

## Homework Equations

Vf = Vi + a*t
x = Vi*t + 0.5*a*t^2
Vf^2 = Vi^2 + 2a*x
Hint: Since the driver starts with a speed that is greater than the speed limit, his final speed will need to be less than the speed limit in order for the measured average speed to equal the speed limit.

I have no idea how to start this.
help!

Well, the average speed is given. And the initial speed. From that you can find the final speed.

Knowing Vi and Vf, you should be able to use one of those formulas to find the acceleration.

You already have the distance to be traveled, and the beginning and final velocity. Plug and chug

Since you know the speed limit and the distance, you can first calculate how long it will take to get from point A to B. Once you know this time it will reduce the number of variables you have to deal with.

Mk said:
You already have the distance to be traveled, and the beginning and final velocity. Plug and chug

You're not given the final speed are you? I don't think you necessarily need to calculate it either.

zooboodoo said:
You're not given the final speed are you? I don't think you necessarily need to calculate it either.
Ah, I read the problem wrong, 19.6 is the average speed, not the final.
But ok, how is your way quicker than finding Vf=19.6*2-28.8 and then continuing on?

Sweeeet. Thank you. That helped a lot. So simple, yet I was making it difficult on myself.

## What is deceleration?

Deceleration is the rate at which an object's velocity decreases over time. It is the opposite of acceleration, which is the rate at which an object's velocity increases.

## How is deceleration measured?

Deceleration is typically measured in meters per second squared (m/s^2) or feet per second squared (ft/s^2). This unit represents the change in velocity per second.

## What factors affect the deceleration of a car?

The deceleration of a car can be affected by several factors, including the car's mass, the road conditions, and the braking force applied by the driver.

## How does deceleration relate to braking?

Deceleration is directly related to braking because when a car brakes, it experiences a negative acceleration, meaning its velocity decreases. The greater the deceleration, the quicker the car will come to a stop.

## Can deceleration be negative?

Yes, deceleration can be negative. This occurs when an object's velocity decreases in the opposite direction of its motion. For example, when a car is moving forward and then reverses its direction, it experiences negative deceleration.

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