# Kinematics Car velocity Problem

• hiineko
In summary: That's a wrap for this post. In summary, the conversation discusses finding the initial velocity and constant acceleration of a green car moving towards a red car, with the help of equations and given information. The solution shows that the initial velocity is 3.60 m/s and the (constant) acceleration is 5.06 m/s^2, with both values having negative signs to indicate the direction of the green car's movement.
hiineko

## Homework Statement

In the figure here, a red car and a green car move toward each other in adjacent lanes and parallel to an x axis. At time t = 0, the red car is at xr = 0 and the green car is at xg = 223 m. If the red car has a constant velocity of 20.0 km/h, the cars pass each other at x = 43.1 m. On the other hand, if the red car has a constant velocity of 40.0 km/h, they pass each other atx = 76.9 m. What are (a) the initial velocity and (b) the (constant) acceleration of the green car? Include the signs.

[/B]

## The Attempt at a Solution

eq 1 = 179.9=Vo(7.75)+1/2a(7.75)^2
eq 2 = 146.1=Vo(6.92)+1/2a(6.92)^2

insert 2 to 1

Vo = 146.1-1/2a(6.92)/(6.92)

179.9=(146.1-1/2a(6.92)/(6.92))(7.75)+1/2a(7.75)^2

got a = 5.06 m/s^2
and vo as 3.60

is my answer right?

You could explain where all those numbers in equation 1 and 2 come from, that makes it easier to understand the solution.
Did you plug the result back into those equations to check?

mfb said:
You could explain where all those numbers in equation 1 and 2 come from, that makes it easier to understand the solution.
Did you plug the result back into those equations to check?

Vr = 20km/h = 5.56m/s x = 43.1
v=d/t -> t=d/v = 43.1/5.56=7.75s
xgreencar - x = 223 - 43.1 = 179.9

179.9=vo(7.75)+1/2a(7.75)^2

same procedure to eq. 2

Sorry but I need a bit help here
*is my answer right

I suggested a way you can test your answer yourself.

Yes it is right. Well, several units are missing.

Edit: oh right, forgot about the signs.

Last edited:
Check signs per original problem statement.

mfb said:
I suggested a way you can test your answer yourself.

Yes it is right. Well, several units are missing.

Edit: oh right, forgot about the signs.

That's one thing that bothers me I need signs how do I know what signs will I use? I just got a positive does it mean I'll use + sign?

hiineko said:
That's one thing that bothers me I need signs how do I know what signs will I use? I just got a positive does it mean I'll use + sign?
On the X axis,which way is the green car going?

insightful said:
On the X axis,which way is the green car going?

So 5.06 and 3.61 will be put a - sign on it? If that's what you meant

Correct, if velocity and acceleration are in the (defined) negative direction, they will have negative values.

insightful said:
Correct, if velocity and acceleration are in the (defined) negative direction, they will have negative values.

Okay thank you! Off to my next question in my next post see you there lol kidding Thankyouu

## 1. How do I calculate the velocity of a car using kinematics?

To calculate the velocity of a car using kinematics, you will need to know the initial velocity, final velocity, and time taken for the car to change its velocity. The formula for calculating velocity is v = (vf - vi) / t, where v is velocity, vf is final velocity, vi is initial velocity, and t is time. Plug in the values and solve for velocity to get your answer.

## 2. Can I use kinematics to determine the acceleration of a car?

Yes, kinematics can be used to determine the acceleration of a car. The formula for acceleration is a = (vf - vi) / t, where a is acceleration, vf is final velocity, vi is initial velocity, and t is time. By plugging in the values for velocity and time, you can calculate the acceleration of the car.

## 3. What are the units for velocity and acceleration in kinematics?

Velocity is typically measured in meters per second (m/s) or miles per hour (mph). Acceleration is measured in meters per second squared (m/s^2) or feet per second squared (ft/s^2).

## 4. How does the motion of a car affect its velocity?

The motion of a car, such as speeding up, slowing down, or changing direction, will directly affect its velocity. If the car is accelerating, its velocity will increase. If the car is decelerating, its velocity will decrease. If the car is moving in a straight line at a constant speed, its velocity will remain the same.

## 5. Can kinematics be used to predict the future velocity of a car?

Yes, kinematics can be used to predict the future velocity of a car. By knowing the initial velocity, acceleration, and time, you can use the formula v = vi + at to calculate the velocity at any given time in the future. However, external factors such as friction and air resistance may affect the actual velocity of the car.

• Introductory Physics Homework Help
Replies
57
Views
943
• Introductory Physics Homework Help
Replies
7
Views
3K
• Introductory Physics Homework Help
Replies
3
Views
2K
• Introductory Physics Homework Help
Replies
2
Views
910
• Introductory Physics Homework Help
Replies
5
Views
4K
• Introductory Physics Homework Help
Replies
33
Views
3K
• Introductory Physics Homework Help
Replies
29
Views
2K
• Introductory Physics Homework Help
Replies
4
Views
2K
• Introductory Physics Homework Help
Replies
3
Views
704
• Introductory Physics Homework Help
Replies
5
Views
7K