Edexcel Physics

It is a past paper question that I can not do. It is about a car going off a hump-backed bridge
When the car is driven over the bridge it follows part of a vertical circle of radius 25.0m centred at O below the bridge.
The mass of the car is 925kg.
If the car is driven across the bridge repeatedly, at gradually increasing speeds, it is found that, above a certain critical speed, the car loses contact with the road at A, and "takes off". Explain why this happens.
(Help with this bit is needed :redface:

)

Calculate the critical speed for this particular bridge.
(HEEEEELP)

Final bit is, An object which is in free fall is said to be "apparently weightless". Explain what this means , illustrating your point with reference to situation described in this question.

Thanks for anyone who can help me.

Reply 1

idiopathic

15

lgs98jonee

It is a past paper question that I can not do. It is about a car going off a hump-backed bridge
When the car is driven over the bridge it follows part of a vertical circle of radius 25.0m centred at O below the bridge.
The mass of the car is 925kg.
If the car is driven across the bridge repeatedly, at gradually increasing speeds, it is found that, above a certain critical speed, the car loses contact with the road at A, and "takes off". Explain why this happens.

(Help with this bit is needed :redface:

)

I think it's because the weight of the car is the centripetal force, which is not enough to keep the car in circular motion.

lgs98jonee

Calculate the critical speed for this particular bridge.
(HEEEEELP)
Final bit is, An object which is in free fall is said to be "apparently weightless". Explain what this means , illustrating your point with reference to situation described in this question.

because the only force acting on the object is its weight.

is your exam tomorrow too? What's "critical speed"?

Reply 2

Economist

11

endeavour

I think it's because the weight of the car is the centripetal force, which is not enough to keep the car in circular motion.

because the only force acting on the object is its weight.

is your exam tomorrow too? What's "critical speed"?

Yea thats right. It appears to be weightless when it 'takes off' as the only force acting it its weight so its in free fall

Reply 3

XXXNICEGUYXXX

2

jan 04
damn hard paper

Reply 4

El Stevo

11

the critical speed is the speed at which there is no overall force acting on the car

Reply 5

mr_tomus

1

Might be a abit late now because i'm guessing you did the exam this morning like me.

It takes off because the reaction force (925g at rest) is zero because the weight force is required for centripetal force.

Critical Speed
mv²/r = 925g

mv²/r = 9074.25

v² = (9074.25r)/m

v = √245.25

Apparently weightless because there is no reaction force on the car....

Edexcel Physics

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