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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
Question 6
The speed limit on many roads in towns is 13.5 m/s Outside schools this speed limit is often reduced by one-third. Calculate the reduced speed limit. Reduced spee... show full transcript
Worked Solution & Example Answer: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
Step 1
Calculate the reduced speed limit.
Answer
To calculate the reduced speed limit, we need to reduce the original speed limit of 13.5 m/s by one-third. This is done as follows:
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Calculate one-third of 13.5 m/s: [ \frac{1}{3} \times 13.5 = 4.5 \text{ m/s} ]
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Subtract this value from the original speed limit: [ 13.5 - 4.5 = 9.0 \text{ m/s} ]
Thus, the reduced speed limit is 9.0 m/s.
Step 2
Explain one other advantage of a reduced speed limit.
Answer
One advantage of a reduced speed limit is that it can reduce stopping distances. When vehicles travel at lower speeds, the distance required to come to a complete stop is less, which enhances safety and reduces the likelihood of accidents. Additionally, a lower speed gives drivers more time to react to unforeseen circumstances, such as pedestrians or other obstacles.
Step 3
Calculate the minimum braking distance for the car at the speed it passed the speed camera.
Answer
We need to calculate the speed of the car first:
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Used the distance traveled and time: [ v = \frac{d}{t} = \frac{14 \text{ m}}{0.70 \text{ s}} = 20 \text{ m/s} ]
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Next, calculate the initial and final velocities, where the car is coming to a stop, so final velocity ( v_f = 0 ): [ u = 20 \text{ m/s},\ v_f = 0 ]
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Now use the formula relating acceleration (deceleration in this case), initial velocity, and distance: [ v^2 = u^2 + 2as\ 0 = (20)^2 + 2(-6.25)s\ ] Rearranging: [ 400 = 12.5s\ s = \frac{400}{12.5} = 32 ext{ m} ]
Thus, the minimum braking distance is 32 m.
Step 4
Explain why the empty van has a shorter stopping distance than the full van when driven at the same speed.
Answer
The empty van has a shorter stopping distance because it has less mass compared to the full van. When the mass is reduced, the braking force applied will result in a greater deceleration. This is due to Newton's second law, which states that acceleration is inversely proportional to mass for a given force. As a result, less braking distance is required to bring the lighter empty van to a stop compared to the heavier full van.