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# mechanics slope question Watch

1. Hi, can anyone help me on this question?
A car and trailer(900kg and 250kg) are moving down a slope inclined at 3 degrees to the horizontal. The resistances to motion of the car and trailer are 150N and 600N. The driving force exerted by the car is 980N.
Find:
a) acceleration of car and trailer - i said 12ms^-2.. is this right?
b) pulling force exerted on the trailer ( and what is this?)

Many thanks!
2. (Original post by igloo1)
Hi, can anyone help me on this question?
A car and trailer(900kg and 250kg) are moving down a slope inclined at 3 degrees to the horizontal. The resistances to motion of the car and trailer are 150N and 600N. The driving force exerted by the car is 980N.
Find:
a) acceleration of car and trailer - i said 12ms^-2.. is this right?
b) pulling force exerted on the trailer ( and what is this?)

Many thanks!
Part (a)
I do not get for part (a). If you consider the car and trailer as a combined system, their mass is 1150 kg. Assuming the acceleration was and using F = ma gives a net force of 13,800 N, which is more than ten times the driving force on the car. Considering that there is a resistive force on each object, and that the slope is only 3 degrees, I think you will agree that the acceleration is a bit much.

I would suggest drawing a diagram with all the forces and angles labelled.

Part (b)
The situation you have described is not clear about there being any attachment between the car and trailer, but I would assume that they mean for there to be a rod/rope joining the two. Therefore the car will provide a force on the trailer and vice versa. To find that force, you consider the forces on the car and the van separately. You will probably need the result from (a).
3. (Original post by Brister)
Part (a)
I do not get for part (a). If you consider the car and trailer as a combined system, their mass is 1150 kg. Assuming the acceleration was and using F = ma gives a net force of 13,800 N, which is more than ten times the driving force on the car. Considering that there is a resistive force on each object, and that the slope is only 3 degrees, I think you will agree that the acceleration is a bit much.

I would suggest drawing a diagram with all the forces and angles labelled.

Part (b)
The situation you have described is not clear about there being any attachment between the car and trailer, but I would assume that they mean for there to be a rod/rope joining the two. Therefore the car will provide a force on the trailer and vice versa. To find that force, you consider the forces on the car and the van separately. You will probably need the result from (a).

Thank you, have solved it now.

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