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# Force Diagrams and motion - HELP PLEASE! watch

1. A car of mass M pulls a trailer of mass m along a straight level road at constant speed. The car experiences a resistance to motion of 5000 N and the trailer feels a resistance to motion of 1000 N.
(i) Draw diagrams showing all of the forces acting on the car and on the trailer.
(ii) By considering the forces on the whole system of car and trailer, find the
driving force in the engine.
(iii) By considering the forces on the trailer only, find the tension in the towbar.

2.Attachment 751872
In the diagram above, mass m1 lies on a rough horizontal table and is connected to masses m2 and m3, where m3 > m2, by light inextensible strings passing over smooth pulleys.
(i) Draw diagrams showing all of the forces acting on each of the masses.
(ii) Assuming that the frictional force is large enough to prevent the system from moving, find expressions for the tension in each string and the frictional force.
2. (Original post by KateA_12345)

1. A car of mass M pulls a trailer of mass m along a straight level road at constant speed. The car experiences a resistance to motion of 5000 N and the trailer feels a resistance to motion of 1000 N.
(i) Draw diagrams showing all of the forces acting on the car and on the trailer.
(ii) By considering the forces on the whole system of car and trailer, find the
driving force in the engine.
(iii) By considering the forces on the trailer only, find the tension in the towbar.

2.Attachment 751872
In the diagram above, mass m1 lies on a rough horizontal table and is connected to masses m2 and m3, where m3 > m2, by light inextensible strings passing over smooth pulleys.
(i) Draw diagrams showing all of the forces acting on each of the masses.
(ii) Assuming that the frictional force is large enough to prevent the system from moving, find expressions for the tension in each string and the frictional force.
Welcome to TSR, and do have a read of the posting guidelines - sticky thread at top of forum.

What have you been able to do so far? Diagram? Thoughts?
3. (Original post by ghostwalker)
Welcome to TSR, and do have a read of the posting guidelines - sticky thread at top of forum.

What have you been able to do so far? Diagram? Thoughts?
Thanks for the reply, its really question 1 part 2 and 3 I could do with some help on. I've managed question 2 now but I don't know what to do for part 2 and 3 of question 1.
4. (Original post by KateA_12345)
Thanks for the reply, its really question 1 part 2 and 3 I could do with some help on. I've managed question 2 now but I don't know what to do for part 2 and 3 of question 1.
Part 2.

We consider the system as a whole, so we're not interested in internal forces, such as those in the towbar.

Since the vehicles are moving at constant speed, i.e acceleration is zero, then via F=ma, the sum of forces acting must be zero.

So, driving force = sum of resistive forces.

Part 3.

Can you now have a go at this yourself?
5. (Original post by ghostwalker)
Part 2.

We consider the system as a whole, so we're not interested in internal forces, such as those in the towbar.

Since the vehicles are moving at constant speed, i.e acceleration is zero, then via F=ma, the sum of forces acting must be zero.

So, driving force = sum of resistive forces.

Part 3.

Can you now have a go at this yourself?
Thanks! Thats helped I think I've got it now!

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