-
The velocity at A will be 0 as the car isn’t moving but the car however has very high potential energy at A.
The potential energy that the car has, can be calculated as follows:
Mass of the car x Gravitational pull x Height
(This can also be written as mgh)
The gravitational pull on the car is approx -10 m/s on the earth
As the car starts to go, along this potential energy now changes to kinetic energy, which is worked out by the following equation:
½ Mass of the car x Velocity squared
(This can be written as ½ mv )
So now the whole of the cars energy =kinetic energy + potential energy
At A on the diagram the potential energy (mgh) is equal to the kinetic energy (½ mv ) at B.
The equation for this is:
mgh = ½ mv Therefore the two Ms will cancel out and leave the new equation as h = v - As you can see here h is proportional to v
2g
It is also correct to say that the maximum velocity of the car will be at B.
The average velocity is calculated as: DISTANCE
TIME
-So from this equation 2x this will simply give the Maximum velocity and again squaring this value will give you the maximum velocity squared
5) Method for doing my investigation
A
B C
Set up experiment is set up exactly as it is in my prediction.
- Firstly, place the car with the front wheels on the line you are starting from. In this case make this 10 cm up from the bottom of the slope, working 10 cm up each time. Mark the measurements clearly on the slope with chalk.
-
Without any of your own force giving the car a push, let the car go, from the 1st height you have decided upon –10 cm (which will be somewhere along point A on the diagram)
- When the cars front wheels get to the start of the run-out, with a stopwatch, begin timing how long it takes for the car to travel from the start of the run-out to where the car stops. (on the diagram you can see that you will be timing from point B – point C)
- Along the run-out should be either a metre stick or a tape measure to take the measurements from, as the car stops. Making sure the same person does the timing each time, otherwise the test isn’t fair.
- Repeat the results for the particular height until you get a group of close results that you are able to get a reliable average from.
- Do the same for each height up the slope by repeating a-c for all of them.
- Once you have a final set of results in a neat table. A graph can then be drawn from this and it is clear to check whether your prediction is true.
6) Fair test
To make this a fair test I must keep the following things the same:
- The gradient of the slope at all times.
- The car you have decided to use
- The person doing the timing
- The type/material of the surface of the ramp
- Whether you are measuring from the front or back wheels of the car
7) Results
We found that our prediction is true and by drawing a graph it is now clear to see this. Along the bottom of the graph will be the height and up the side of the graph is the Velocity squared. From knowing that the height is proportional to the velocity squared the graph should look something like this-
If there are any anomalous results then these should be repeated again.
Conclusion
At the start of our investigation the car we used was giving us unreliable results and so we decided to do the whole investigation from the beginning but with a different car and also with a different person doing the timing .We definitely made the right decision as we then got better results. From these results we found that the line of best fit on the graph showed a positive correlation, which is what we wanted. However the results weren’t quite right so we re-tested them and found we got better, more reliable results that we could then work from. From the new results we plotted them on a graph and found that what we got was perfect and agreed with our prediction at the start.
