Physics homework-momentum and impulse-

[housedog1]

hello I'm struggling with physics this year at school i found this site looks great if this is a bad 1st post i won't be to surprised any way here's my problem...

Homework Statement

A Car A (with a mass of 750Kg) is travailing at 30 m s-1 and collides head on with car B travailing at 20 m s-1 with a (mass 1600kg) in the opposite direction

Homework Equations

A Calculate the magnitude of the momentum of each car before crashing

B If the two cars lock together in the crash, in which direction will they be moving immediately after the collision?

C
I Calculate the initial speed of the combined wreck immediately after the collision

II why dose the speed quickly reduce to zero?

The Attempt at a Solution

...ok so far i have drawn a picture like so...

(carA)----------------><---------(carB)
|750kg|-----|30ms-1|-------|20ms-1|--|1600kg|

lol i have no idea...also i have the answerers in the back of the book but that's not learning so that's why i came here :)

any help would be great! even if you could point me in the right direction

Thanks
housedog1

 

[rl.bhat]

use the law of conservation of linear momentum. Since the two cars are moving in the opposite direction, you have to use proper sign for each momentum.

 

[nlightner]

Hello housedog1,

I'm glad you found this site helpful! Physics can be a challenging subject, but with practice and some helpful guidance, you can definitely improve. Let's take a look at your problem and work through it together.

First, let's start with the basics. Momentum is a physical quantity that describes the motion of an object. It is defined as the product of an object's mass and its velocity. In equation form, it looks like this:

p = mv

Where p is momentum, m is mass, and v is velocity.

Now, let's apply this to the problem at hand. We have two cars, A and B, traveling towards each other. We are given their masses and velocities, and we need to calculate their momenta before the collision. To do this, we simply plug the given values into the equation:

pA = (750kg)(30m/s) = 22500 kg m/s

pB = (1600kg)(20m/s) = 32000 kg m/s

So, we now know the momentum of each car before the collision. But what happens during and after the collision? This is where impulse comes into play.

Impulse is a change in momentum that occurs over a period of time. In equation form, it looks like this:

I = Ft

Where I is impulse, F is the force applied, and t is the time over which the force is applied. In this case, the force is the force of the collision between the two cars.

Now, let's move on to the rest of the problem. We are asked to determine the direction in which the cars will be moving after the collision. Since they are traveling towards each other at the same speed, they will collide and lock together, moving in the same direction. This is because the total momentum of the system (the two cars) must be conserved. In other words, the total momentum before the collision must equal the total momentum after the collision. So, the cars will be moving in the direction of car A, since it has a higher momentum.

Next, we are asked to calculate the initial speed of the combined wreck immediately after the collision. To do this, we use the same equation as before, but this time we use the total mass of the two cars and their combined momentum:

p = mv

22500 kg m/s + 32000 kg m/s = (750kg + 1600kg)v