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# Mechanics Help watch

1. I don't know how to solve this question, which is to do with the Newton's Law:

A car of mass 1 tonne exerts a driving force of 2.5kN when pulling a trailer of mass 400 kg along a level road. The car and trailer start from rest and travel 18 m in the first 6 s of motion. If the resistances on the car and trailer are 1000xN and 400xN respectively, find the value of the constant x.

I worked out the acceleration and final velocity using the SUVAT formulae, which gave me 1 for the acceleration and 6 for the final velocity, and I have no clue on what to do now

Thanks in advance,
Mincan
2. Use F = ma ?
3. Write down work and energy equations.
4. Ok, just so you know 1 tonne = 1000 kg

You have already have the acceleration of the car and trailer.
So now just use Newton's second law (F=ma) to work out the vaule of x
(the combined mass of the car and trailer is 1400kg)
5. You use F=ma

SO the combined mass is 1400kg and the acceleration is 1ms^-2
so the overall force is 1400N

Since the car is exerting a driving force of 2500N. It's 2500 - (1000x + 400x) = 1400
Solve to find x.
6. (Original post by Papkin)
Write down work and energy equations.
Don't do this.
7. I understand now

Thank you everyone!
8. (Original post by Mr M)
Don't do this.
I suppose suggesting using what he has already done to solve the problem his own way is much better than just giving him entirely different method, don't you?
9. (Original post by Papkin)
I suppose suggesting using what he has already done to solve the problem his own way is much better than just giving him entirely different method, don't you?
I didn't really understand your question but the OP is clearly just starting M1 and work and energy methods are M2 in most specifications.
10. (Original post by Papkin)
I suppose suggesting using what he has already done to solve the problem his own way is much better than just giving him entirely different method, don't you?
Urm no, it's totally unnecessary.

And F = ma is using what he has already done - he has found out a!
11. (Original post by Thrug)
Urm no, it's totally unnecessary.

And F = ma is using what he has already done - he has found out a!
I'm having a bad day, everyone is either refusing to listen to anything I say or squabbling with me! Thanks for the support.
12. (Original post by Mr M)
I'm having a bad day, everyone is either refusing to listen to anything I say or squabbling with me! Thanks for the support.
Anytime.

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