Conserved momentum (car accident)

In summary, the collision between a blue car with a mass of 2000 kg and a yellow truck with a mass of 9000 kg, traveling at 7 m/s from the south and west respectively, results in a clump with a combined mass of 11000 kg sliding at an angle of 43° north of east. Using conservation of momentum, the final velocity of the clump can be determined by dividing the total momentum by the total mass and multiplying it by the components of the velocity vector.
  • #1
mujadeo
103
0

Homework Statement


A blue car with a mass of 2000 kg and a yellow truck with mass 9000 kg enter an intersection. The truck comes from the south at vtruck = 7 m/s, and the car comes from the west. When the two collide they stick together and slide at an angle of q = 43° north of east.

What is the speed of the pair after the collision?


Homework Equations


how can i do anything with question without speed of the blue car?
i know p=63000, and angle plays into it, but can't figure this out
please help

The Attempt at a Solution

 
Physics news on Phys.org
  • #2
mujadeo said:

Homework Statement


A blue car with a mass of 2000 kg and a yellow truck with mass 9000 kg enter an intersection. The truck comes from the south at vtruck = 7 m/s, and the car comes from the west. When the two collide they stick together and slide at an angle of q = 43° north of east.

What is the speed of the pair after the collision?


Homework Equations


how can i do anything with question without speed of the blue car?
i know p=63000, and angle plays into it, but can't figure this out
please help

The Attempt at a Solution


Use conservation of momentum... momentum is conserved along any axis... so momentum is conserved in the north/south direction... and momentum is also conserved in the east/west direction... Write the equations out for conservation of momentum in the north/south direction, and also in the east/west direction... you'll have to use some trigonometry... You'll have two equations with two unknowns...
 
  • #3
OK, so north south is y and east west is x
p in y before collision is 63000
i don't understand p is conserved in both directions?
the combined mass can't chaneg (=11000kg) and it moves with only one speed and p is the same after collision as it was before.
So i don't understand this
 
  • #4
mujadeo said:
OK, so north south is y and east west is x
p in y before collision is 63000
i don't understand p is conserved in both directions?
the combined mass can't chaneg (=11000kg) and it moves with only one speed and p is the same after collision as it was before.
So i don't understand this

Yes, the combined mass is 11000kg. And there's an unknown final velocity call it vf... and it's moving at an angle of 43 degrees. So the momentum after the collision has a magnitude of 11000*vf... Draw a picture of this vector... Can you divide up this vector into a horizontal(east/west) and vertical component(north south)? Use cos and sin...
 
  • #5
yes i understand about getting the components of vectors, but what components are they, speed or momentum. and how can that tell me the speed?
 
  • #6
Since you CAN get components of vectors, I would suggest you start doing so. They are velocity AND momentum. And as learningphysics points out momentum is conserved along both axes. What do you get from the north-south axis? Your doubts you will get anything are stopping you from continuing.
 
  • #7
Dick said:
Since you CAN get components of vectors, I would suggest you start doing so. They are velocity AND momentum. And as learningphysics points out momentum is conserved along both axes. What do you get from the north-south axis? Your doubts you will get anything are stopping you from continuing.

:smile: Yes. The first step is writing out the equations mujadeo. If you're having trouble writing out the 2 conservation of momentum equations, then let us know where you're getting stuck.
 
  • #8
K= 1/2mv^2
p=mv
i am sorry i am not getting what the components are?
should i get x and y components of the total momentum (63000) befor the collision and use that to someone get v??
 
  • #9
what i mean is, take total momentum (which is same cause its conserved) and then multiply by cos43, which will give v in x dire
then mult by sin43 giving v in y
then use trig to find the hyp side (velocity at 43deg)
?

edit -- i forget the divide by the mass step
(i am using p/m = v )
 
  • #10
mujadeo said:
what i mean is, take total momentum (which is same cause its conserved) and then multiply by cos43, which will give v in x dire
then mult by sin43 giving v in y
then use trig to find the hyp side (velocity at 43deg)
?

edit -- i forget the divide by the mass step
(i am using p/m = v )

Yes, that's the right idea... I wouldn't worry about the velocity vector... I'd just deal with the momentum vectors...

So the east-west componenet of momentum would be mf*vf*cos43 and the north-south component would be mf*vf*sin43... where mf is the total mass of the clump after the collision, and vf is the final velocity.

So the total momentum in the east west direction before the collision = total momentum in the east west direction after the collision... and the same idea with the north-south direction...
 
  • #11
OK I got this one nailed
thank you for the help!
 

1. What is conserved momentum in the context of a car accident?

Conserved momentum refers to the principle that the total momentum of a closed system remains constant before and after a collision. In a car accident, this means that the total momentum of the vehicles involved in the collision will remain the same before and after the crash.

2. How does the conservation of momentum apply to car accidents?

In a car accident, the conservation of momentum is demonstrated by the fact that the total momentum of the vehicles involved in the collision will remain constant. This means that the combined mass and velocity of the cars before the collision will equal the combined mass and velocity after the collision.

3. What factors affect the conservation of momentum in a car accident?

The conservation of momentum in a car accident can be affected by several factors, including the mass and velocity of the vehicles involved, the angle of impact, and any external forces acting on the cars during the collision.

4. How is the conservation of momentum related to Newton's laws of motion?

The conservation of momentum is related to Newton's laws of motion, specifically the law of conservation of momentum, which states that the total momentum of a closed system remains constant. This principle is an extension of Newton's first law, also known as the law of inertia.

5. Is the conservation of momentum always observed in car accidents?

In most cases, the conservation of momentum is observed in car accidents. However, in some situations, such as collisions involving external forces or multiple collisions, the conservation of momentum may not be perfectly conserved. In these cases, other factors such as energy dissipation may come into play.

Similar threads

  • Introductory Physics Homework Help
Replies
9
Views
3K
  • Introductory Physics Homework Help
Replies
1
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
6K
  • Introductory Physics Homework Help
Replies
7
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
8K
  • Introductory Physics Homework Help
Replies
4
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
1K
  • Introductory Physics Homework Help
Replies
4
Views
2K
  • Introductory Physics Homework Help
Replies
10
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
987
Back
Top