The speed limit on many roads in towns is 13.5 m/s Outside schools this speed limit is often reduced by one-third - AQA - GCSE Physics Combined Science - Question 6 - 2020 - Paper 2

A reduced speed limit reduces stopping distances, which enhances road safety. This means that drivers have more time to react and can avoid collisions, leading to fewer accidents.

First, we calculate the speed of the car:

Using the formula:

Distance = Speed × Time

We have:

14 m = v × 0.70 s

Thus, v = \frac{14}{0.70} = 20 , (m/s)

Next, we apply the kinematic equation to find the minimum braking distance:

Using the formula:

$v^2 = u^2 + 2as$

Where: v = final velocity (0, since the car stops) u = initial velocity (20 m/s) a = acceleration (negative deceleration = -6.25 m/s²) s = stopping distance

Plugging in the values:

$0 = (20)^2 + 2(-6.25)s$

Rearranging gives us:

$20^2 = 12.5s$

Solving for s:

$s = \frac{400}{12.5} = 32 \, m$

The empty van experiences the same maximum force applied by the brakes as the full van does. However, since the mass of the empty van is less, it has a greater deceleration. Consequently, the braking distance is shorter for the empty van. Furthermore, the kinetic energy of the van (at a given speed) is also less, requiring less work to bring the van to a stop.