# Forces, find net with velocity and distance

• yogoes123
In summary, the 1420kg car traveling at 64.8km/h comes to a stop after 729m. To find the net force, the equation vf^2=vi^2+2ad can be used, where a=0.2222222 and the final answer is 316N.
yogoes123

## Homework Statement

Driver brakes 1420kg car moving at 64.8km/h [W]. Car slows down and comes to stop after 729m [w]

find net force

a=v/t f=ma

## The Attempt at a Solution

t=40.5 a= 0.44

f=1420(0.44) f= 624.8

TB Answer: 316N what am i doing wrong?

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Hi yogoes123. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

Your first mistake is probably in how you worked out that 40.5 secs, as you haven't shown the equation you used.

Last edited by a moderator:
I used v=d/t swapped it around and solved for t=d/v and that gave me 40.5s, is that wrong?

yogoes123 said:
I used v=d/t swapped it around and solved for t=d/v and that gave me 40.5s, is that wrong?
That equation relates time to the distance traveled at a constant speed.

So it would be correct, no? I can't figure out what i did wrong.

yogoes123 said:
f=1420(0.44) f= 624.8

ans is: 316N

what am i doing wrong?
You [somehow] worked out a figure of 624.8N

How to explain that halving?

The TB answer is 316, my answer is 624.8, sorry I didnt make that clear.

yogoes123 said:
So it would be correct, no? I can't figure out what i did wrong.
As I emphasised "at a constant speed". At no time here is the vehicle traveling at a fixed speed, the vehicle is constantly slowing.

To begin over...

you need equations relating distance, initial velocity, final velocity (= 0 here) etc.

So, write down some suitable candidates.

I thought it starts to slow down after the 729m. Are you saying that is it slowing down within 729m?

yogoes123 said:
I thought it starts to slow down after the 729m. Are you saying that is it slowing down within 729m?
At the 729m mark, it is motionless.

Where speed is constant it has acceleration = 0 (for straight line travel).

1 person
Ok I think I got this, I used Vf^2=Vi^2+2ad

Then I did a= 18^2/2/729 and i got 0.2222222 then I used F=ma and got 316, thanks so much for clearing that up.

Good.

## What is a force?

A force is a push or pull that can change the motion or shape of an object. It is a vector quantity, meaning it has both magnitude and direction.

## How do you find the net force?

To find the net force, you need to add up all the individual forces acting on an object. If the forces are acting in the same direction, you add them together. If they are acting in opposite directions, you subtract them.

## What is velocity?

Velocity is the rate of change of an object's position over time. It is a vector quantity, meaning it has both magnitude and direction. It is often measured in meters per second (m/s).

## How is distance related to velocity?

Distance is the total path length an object has traveled. Velocity is the rate of change of an object's position, so it is related to distance in that it tells us how fast an object is covering a certain distance.

## What is the relationship between force, velocity, and distance?

Force, velocity, and distance are all related through Newton's second law of motion, which states that the net force on an object is equal to its mass multiplied by its acceleration. Velocity is related to acceleration, as it is the rate of change of an object's velocity, and distance is related to acceleration, as it is the rate of change of an object's position.

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