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# M1 Question watch

1. A trailer of mass 600 kg is attached to a car of mass 900kg by means of a light inextensible tow-bar. The car tows the trailer along a horizontal road. The resistances due to motion of the car and the trailer are 300N and 150N respectively.

a) Given that the acceleration of the car and trailer is 0.4ms^-2, calculate,
i) the tractive force exerted by the engine of the car,
ii) the tension in the tow - bar.

b) Given that the magnitude of the force in the tow-bar must not exceed 1650N, calculate the greatest possible deceleration of the car.

Got part a) and b), struggling with part c)
a. 1050N.
b.390N

For C, why is the force acting in the same direction as the 150N(if we're looking at the trailer alone). Is it because we assume it's thrust to get the maximum deceleration??
2. (Original post by dont know it)
A trailer of mass 600 kg is attached to a car of mass 900kg by means of a light inextensible tow-bar. The car tows the trailer along a horizontal road. The resistances due to motion of the car and the trailer are 300N and 150N respectively.

a) Given that the acceleration of the car and trailer is 0.4ms^-2, calculate,
i) the tractive force exerted by the engine of the car,
ii) the tension in the tow - bar.

b) Given that the magnitude of the force in the tow-bar must not exceed 1650N, calculate the greatest possible deceleration of the car.

Got part a) and b), struggling with part c)
a. 1050N.
b.390N

For C, why is the force acting in the same direction as the 150N(if we're looking at the trailer alone). Is it because we assume it's thrust to get the maximum deceleration??
you have not posted part c) so we are also struggling
3. (Original post by the bear)
you have not posted part c) so we are also struggling
Oh haha, the answers i listed above were for part i) and ii). I need the answer to part b), sorry.
4. (Original post by dont know it)
A trailer of mass 600 kg is attached to a car of mass 900kg by means of a light inextensible tow-bar. The car tows the trailer along a horizontal road. The resistances due to motion of the car and the trailer are 300N and 150N respectively.

a) Given that the acceleration of the car and trailer is 0.4ms^-2, calculate,
i) the tractive force exerted by the engine of the car,
ii) the tension in the tow - bar.

b) Given that the magnitude of the force in the tow-bar must not exceed 1650N, calculate the greatest possible deceleration of the car.

Got part a) and b), struggling with part c)
a. 1050N.
b.390N

For C, why is the force acting in the same direction as the 150N(if we're looking at the trailer alone). Is it because we assume it's thrust to get the maximum deceleration??
It's because the car is decelerating which means its velocity is reducing, which means that the trailer's speed is reducing, which implies an increased overall force in the opposite direction of motion, so the motion resistance + the tow-bar 'compression'
5. (Original post by RDKGames)
It's because the car is decelerating which means its velocity is reducing, which means that the trailer's speed is reducing, which implies an increased overall force in the opposite direction of motion, so the motion resistance + the tow-bar 'compression'
Ohh, thank you. When I resolve(R-->) for the car though, I get 1050-1650-300=900a. The actual answer is supposed to be 3m/s.
6. (Original post by dont know it)
Ohh, thank you. When I resolve(R--> for the car though, I get 1050-1650-300=900a. The actual answer is supposed to be 3m/s.
Why are you taking away the 1650? It acts (-->) for the car, while it acts (<--) for the trailer. Also since it's slowing down it does not have have to fight the motion resistance forces so that can be ignored by the looks of it.
7. (Original post by RDKGames)
Why are you taking away the 1650? It acts (--> for the car, while it acts (<--) for the trailer. Also since it's slowing down it does not have have to fight the motion resistance forces so that can be ignored by the looks of it.
But then wouldn't you have 1050+1650N=900a, meaning it's accelerating? Also, is that the case all the time(ignoring the resistance forces if it's slowing down), and if it's not, is there a way of knowing when to ignore it?
8. (Original post by dont know it)
But then wouldn't you have 1050+1650N=900a, meaning it's accelerating? Also, is that the case all the time(ignoring the resistance forces if it's slowing down), and if it's not, is there a way of knowing when to ignore it?
Sorry I lost track of this question.

Didn't you say it was decelerating? In which case, acceleration cannot be +ve.

Anyway, I'm off now as it's late so I'll let someone else jump in.
9. (Original post by RDKGames)
Sorry I lost track of this question.

Didn't you say it was decelerating? In which case, acceleration cannot be +ve.

Anyway, I'm off now as it's late so I'll let someone else jump in.
No problem. Thanks for your time.

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