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Momentum question watch

1. Hey, Can anyone point us in the right direction for this question??

A stationary car of mass 800kg is struck by a car with mass 1200kg which is travelling at 10 ms

If the first car continues at 4ms what is the speed if the second car?

Any help would be appreciated?
cheers
2. use the mom equation mom = mass x velocity
3. (Original post by Reptic)
Hey, Can anyone point us in the right direction for this question??

A stationary car of mass 800kg is struck by a car with mass 1200kg which is travelling at 10 ms

If the first car continues at 4ms what is the speed if the second car?

Any help would be appreciated?
cheers
For these kinds of question I'd recommend drawing a diagram with the stuff you know and the stuff you want to find out, and the key to this question is the law of conservation of momentum.
4. (Original post by Reptic)
Hey, Can anyone point us in the right direction for this question??

A stationary car of mass 800kg is struck by a car with mass 1200kg which is travelling at 10 ms

If the first car continues at 4ms what is the speed if the second car?

Any help would be appreciated?
cheers
By conservation of momentum:

5. This is our current thinking...

Before Crash After crash
1200 x 10 + 800 = 12800 Goes to 1200v + (800 x 4)
12800 - 3200 = 9600
9600 / 1200 = 8 ms????
6. (Original post by Reptic)
This is our current thinking...

Before Crash After crash
1200 x 10 + 800 = 12800 Goes to 1200v + (800 x 4)
12800 - 3200 = 9600
9600 / 1200 = 8 ms????
The method is right, but you should think about something in the first line of your calculations. What is the initial momentum of the stationary car?

Spoiler:
Show
The first line was correctly done for you above.
7. Ahhhhh so we've ammended it to...

Before After
1200 x 10 (12000 + 0) goes to 1200 V? + 800 x 4
1200 V? + 3200 = 12000
12000 - 3200 = 8800
8800 / 1200 = 7.3 ms
8. (Original post by Reptic)
Ahhhhh so we've ammended it to...

Before After
1200 x 10 (12000 + 0) goes to 1200 V? + 800 x 4
1200 V? + 3200 = 12000
12000 - 3200 = 8800
8800 / 1200 = 7.3 ms
Yep, well done.
9. (Original post by SeanFM)
Yep, well done.
Nice one cheers mate!

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