# How does the mass of a vehicle affect its stopping distance when brakes are applied?

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Introduction

GCSE Physics coursework

Problem

The problem to be investigated is “how does the mass of a vehicle affect its stopping distance when brakes are applied?” This problem is related to the conservation of energy and will be investigated through a trolley going down a ramp. A simple trolley will be used to represent the vehicle and weights attached to the rear of the trolley via a pulley system will act as the brakes. Throughout the experiment energy will be transferred into many forms but no energy will be lost or gained. As the trolley is raised it gains potential energy, when released down the ramp this energy is converted to kinetic energy. When the trolley hits the horizontal surface all the energy will be kinetic. As the trolley continues to roll the kinetic energy within it, raises the weights on the pulley system. The kinetic energy is therefore converted to potential energy in the weights. The stopping distance of the trolley can be measured, therefore allowing us to measure the potential energy in the trolley.

When any mass is raised it gains gravitational potential energy. The formula used to calculate potential energy is as follows: -

PE = mgh

Potential energy = Mass x Gravitational Pull x Height Raised

If there are no opposing forces acting upon the trolley then kinetic energy should be equal to potential energy. The formula used to calculate kinetic energy is as follows: -

Middle

- The length of the trolley
- The weight of the trolley (without addition of mass)
- The length of the string
- The height from which the trolley is released
- The units of measurement used
- The mass used to stop the trolley (braking force)

These are the control factors in the experiment.

Preliminary work

A preliminary experiment must be carried out ion order to determine the weight that should be used to replicate braking force. To find the most suitable weight for this particular experiment the trolley will be used without additional mass i.e. the mass of the trolley will be kept constant. If the trolley mass is kept constant we can easily see what effect the weight is having on stopping distance. This is vital in order to carry out an experiment where it is possible to make the most accurate observations and where a wide range of results is easily recorded.

By placing a variety of weights on the string and releasing the trolley down the ramp we got an indication of how far the trolley is likely to travel and how much weight will be required to stop the trolley. We experimented with weights in denominations of 1N.

Result

From the preliminary experiment it was possible to conclude that the optimum weight to be used for braking force will be 5N. This allows us to get the greatest range of accurate results.

Prediction

Conclusion

This was the theory on which I based my prediction and it is clearly matched here in the results, as the correlation is strong.

Evaluating Evidence

I think that the method used in this experiment was a good way carrying out the investigation because it enabled us to gain results over a range of trolley weights. This had to be tested during the pilot practical. This combined with the repetition of the experiments meant that we had a wide range of data enabling us to find any anomalous results and find a clear correlation.

What Improvements Would Be Made If Redone?

1. Reduce the friction of the system.

2. Make the trolley more aerodynamic.

3. Electronically measure the stopping point for more accuracy with results.

4. Do the experiment more times.

Accuracy of Results

The results were measured very carefully and to the best of human judgement. I would estimate the results were measured to within the nearest centimetre. This is easily accurate enough to show a clear distance between weights, accurate enough that the repeated results didn’t differ so much as a consequence of this inaccuracy and accurate enough to show the correlation and prove the theory.

Tim Wright 11RS

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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