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Asked by emmagrace to Dalya, Derek, Sarah, Tim, Tom on 19 Jun 2011.
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Dalya Soond answered on 17 Jun 2011:
Depends how fast it is going and how good its brakes are and the conditions of the road.
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Sarah Thomas answered on 17 Jun 2011:
The stopping distance of a lorry is 3 to 6 times longer than a normal car. The problem is their mass. A lorry can weigh between 3.5 and 44 tonnes! Cars usually only weigh between 1 to 3 tonnes. A lorry has a greater stopping distance because it generates far more momentrum and this means that it decelerates more slowly.
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Derek McKay-Bukowski answered on 17 Jun 2011:
Acceleration is a change in speed. To go from slow to fast you need to accelerate. To go from fast to slow you need to accelerate backwards (called decelerating). And to get an acceleration you need to apply a force. The acceleration is equal to this “braking force”, divided by the mass.
Is that that mass that is the key point. The lorry is so much more massive. Compare a 1-tonne car to a 40-tonne lorry. For the same braking power, the lorry’s deceleration time will be 40 times longer.
Fortunately, lorries have huge brakes, so that can stop moderately quickly, but the small brakes of a car, combined with the car’s smaller mass, make it so much easier for the car to stop more quickly.
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Tom Crick answered on 18 Jun 2011:
There are a number of factors: the velocity of the lorry, how heavy it is, how good its brakes are, temperature, whether the surface is wet, what type of tyres, etc…but essentially from a physics perspective you have to decelerate (change the velocity) a moving mass which has momentum (the product of mass and velocity). Compared to a car travelling at the same velocity, it has greater mass so has greater momentum and it will take a greater force to decelerate (see Newton’s laws of motion).
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Tim Millar answered on 19 Jun 2011:
Depends how good the breaks are, how fast its going and how heavy it is.
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