Question

The brakes of an unload lorry of mass 1000 kg will slow it down from 40 to 20 km/h in 7.5 s.How long will they take to stop it from a speed of 30 km/h,if it has taken on a load of 2200 kg

Answer 1

When the brakes are applied, the tyres apply a force on the road as described by the formula F=ma. Assuming the deceleration is constant, you can find it using (vf−vit)/t

Where vf is the final velocity, vi is initial velocity, and t is time.

Once you have the acceleration, a, you can find the force of the brakes and then use that to find the deceleration of the 3200 kg lorry.

With that new a, you can then find the time taken to slow to v=0 using the following

v=u+at

Where u is initial velocity so you can rewrite the equation as

u = at−u

Now you need to put in all the values and you will get the answer

Answer 2

Answer:

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