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# Really URGENT maths help watch

1. I need to answer some questions for Maths : Mechanics

A car of mass 1200kg pulls a trailer of mass 400kg along a straight horozontal road. The car and trailer are connected by a tow rope modelled as a light inextensible rod. The engine of the car provides a constant driving force of 3200N. The horizontal resistances of the car and the trailer are proportional to their respective masses. Given that the acceleration of the car and trailer is 0.4 ms-2 ,

a) Find the resistance to motion on the trailer
b) Find the tension of the tow-rope

HELP will be kindly appreciated. Thank you
2. First, to get started, treat the truck and trailer as one thing.

You know what the total mass is, you know what the acceleration is so you can work out the total unbalanced force on the whole thing together.

Knowing what the engine force is, you can therefore calculate the total resistive force.

Then you can break that up since you know it's divided between th two according to their mass.

Then for the second part, you can use what you now know to be the resistive force on the trailer. The total resultant force on the trailer depends on the Tension in the tow bar and the resistive force, and provides the acceleration of the trailer (trailer only this time)

Does that help enough?
3. I reallllllllllllly neeeeeeeeeeeed heeeeeeeeeeeeeeeelp. Thank you
4. (Original post by phys981)
First, to get started, treat the truck and trailer as one thing.

You know what the total mass is, you know what the acceleration is so you can work out the total unbalanced force on the whole thing together.

Knowing what the engine force is, you can therefore calculate the total resistive force.

Then you can break that up since you know it's divided between th two according to their mass.

Then for the second part, you can use what you now know to be the resistive force on the trailer. The total resultant force on the trailer depends on the Tension in the tow bar and the resistive force, and provides the acceleration of the trailer (trailer only this time)

Does that help enough?

Your help was very useful. Thanks. The one thing I didn't understand is the division, should I split them into ratios or?
5. In the end, you don't need the Resistive force for the car, just the trailer.

So say the trailer has 400/(1200+400) = 1/4 the total mass. so 1/4 the total resistive force.

EDITED _ sorry. used the wrong mass for the car.
6. (Original post by phys981)
In the end, you don't need the Resistive force for the car, just the trailer.

So say the trailer has 400/(1200+400) = 1/4 the total mass. so 1/4 the total resistive force.

EDITED _ sorry. used the wrong mass for the car.

No it's alright. I figured that out. But honestly, Thank you for explaining.
7. Can you explain how to work out the total unbalanced force please?Thank you
8. (Original post by doughnut1)
Can you explain how to work out the total unbalanced force please?Thank you
You just add the forces, but treat those going forward as positive and backward as negative.

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