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The Braking Distance of a Car - Mass.

The total stopping distance = thinking distance + braking distance.

Changing the
mass of a car does not
change the thinking distance

but

the braking
distance is changed as the
mass of a car changes.

See also the calculation of the force
need to stop a moving car

using kinetic
energy or momentum.

How does
Mass affect the Braking
Distance of a Car?

The braking
distance of a car increases as the mass increases.

The two calculations below show how

doubling the mass changes
the braking
distance of a car.

Q1. The
brakes of a car
apply a force of 1500N.

If the car has a mass of 750 kg, what
is its acceleration?

(How quickly does it slow down?)

A1. Use F = m x a

or a = F ÷ m

a =
1500 ÷ 750

= 2 m/s^{2}.

Strictly
speaking we would call the acceleration
-2 m/s^{2}

because the car is slowing down.

Q2. The
brakes of the car apply the same force of 1500N.

If the car has double the mass at
1500 kg, what is its acceleration?

(How quickly does it slow down?)

A2. Use F = m x a

or a = F ÷ m

a =
1500 ÷ 1500

= 1 m/s^{2}.

After we have
doubled the mass of the car and

applied the same force from the brakes,

the car is now slowing down at only
half the rate.

The
car with twice
the mass will take twice as
long to stop

(requiring twice the braking distance - see kinetic energy).

Notice that
the rate of negative
acceleration (slowing down)

only depends on the force of the
brakes and the mass of the car,

not how fast the car is
going.

A faster moving
car will take further to
stop for the same acceleration

(the same rate of slowing down,
see the previous
page).

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