# Calculate velocity of stopping car

• Lizi
In summary, the car has a initial velocity of u and after traveling a distance of 2 d it has a velocity of v. The equation that relates u,v,s and a is v=at/(2a).
Lizi

## Homework Statement

A car moving at 20m/s starts decelerating, travels distance d, and stops. Find the car’s velocity at distance d/2.

## The Attempt at a Solution

my brain is fried. I feel like I’m missing something obvious but I just don’t get it.

I suppose you should assume a constant deceleration

Lizi said:

## Homework Statement

A car moving at 20m/s starts decelerating, travels distance d, and stops. Find the car’s velocity at distance d/2.

## The Attempt at a Solution

my brain is fried. I feel like I’m missing something obvious but I just don’t get it.

It was a bit of a brain 'fry' !

Time 'reversing' so that we have acceleration from 0 m/s instead of deceleration from 20 m/s:

$$d = ½at^2 ⇒ \frac{d}{2} = ½a\left({\frac{t}{\sqrt{2}}}\right)^2 ⇒v=\frac{at}{\sqrt{2}}$$

neilparker62 said:
It was a bit of a brain 'fry' !

Time 'reversing' so that we have acceleration from 0 m/s instead of deceleration from 20 m/s:

$$d = ½at^2 ⇒ \frac{d}{2} = ½a\left({\frac{t}{\sqrt{2}}}\right)^2 ⇒v=\frac{at}{\sqrt{2}}$$

But since you don't know ##a## you can't obtain ##t##, so you stick with two unknowns. I think the question should be solved independent of the time ...

Edit: This cross posted with some of the above;

It gives you the initial velocity (u) and asks you to find the cars velocity (v) after traveling a distance (s = d/2). What equation relates u,v,s and a?

You aren't given the acceleration (a) but you can work it out from the first part of the problem statement.

stockzahn said:
But since you don't know ##a## you can't obtain ##t##, so you stick with two unknowns. I think the question should be solved independent of the time ...
at = ?

neilparker62 said:
at = ?

Still, I think the medthod @CWatters proposes is the preferred one. Additionally it should be the OP's task to solve it ...

guys, I figured it out using the d=(v2-u2)/(2a) formula.
Thank you all so much

neilparker62

## 1. How is velocity calculated for a stopping car?

The velocity of a stopping car can be calculated by dividing the initial velocity (speed at the beginning of braking) by the time it takes for the car to come to a complete stop.

## 2. What factors affect the velocity of a stopping car?

The velocity of a stopping car can be affected by factors such as the initial velocity, the mass of the car, the braking force applied, and the coefficient of friction between the tires and the road surface.

## 3. Can the velocity of a stopping car be negative?

Yes, the velocity of a stopping car can be negative if it is moving in the opposite direction of the initial velocity. This is known as deceleration or negative acceleration.

## 4. How does the velocity of a stopping car relate to its kinetic energy?

The velocity of a stopping car is directly proportional to its kinetic energy. This means that the higher the velocity, the greater the kinetic energy, and the longer it will take for the car to come to a complete stop.

## 5. What is the difference between velocity and speed for a stopping car?

Velocity and speed are often used interchangeably, but they have different meanings. Velocity is a vector quantity that includes both the speed and direction of an object, while speed is a scalar quantity that only refers to the magnitude of the object's motion. When a car is stopping, its velocity is changing as it slows down, but its speed is decreasing at a constant rate.

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