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# Physics URGENT HELP!!!!! GCSE Watch

1. (Original post by Wolfram Alpha)
What have you tried so far? What do you think you could do/try?
2. I think the answer is 3000 N
3. So you know that F=M * A, so if you have been given the mass of car and caravan, just minus the mass of the car to find the mass of the caravan. Then you have been given the deceleration so just times 1000 (the mass of the caravan) by 3 (deceleration) which is 3000 N so you were right. I am a bit confused however why the deceleration wouldn't be converted to minus when put in the calculation as acceleration! if you need more help just watch this, https://www.youtube.com/watch?v=6GYx...E3947A&index=1
Literally it has saved my life!
4. (Original post by Wolfram Alpha)
3000N ??
1. i first subtracted the mass of the caravan and car which is 1000kg
2. i used the formula force = mass x acceleration
-> force = 1000kg x 3 m/s^2 making the answer 3000N

i could be wrong tho lol
5. (Original post by Wolfram Alpha)
Treat as one single body. If the deceleration with the caravan attached is 3m/s2, then that's the deceleration of the whole combined body (car plus caravan - assuming the tow bar isn't stretchy!)

F(resultant)=ma
=2000 x 3
=6000N to decelerate both.

But we know the car is already providing 4000N. So the caravan is contributing 2000N of braking force.

The trick to questions like this is to define your 'body.'

Hope that helps.

(p.s. it gets a little complicated to treat the caravan separately, because there are forces from the car acting upon it which would need calculating. Although it's possible to do it this way, It is best to treat both as a single decelerating system.)

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Updated: June 15, 2016
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