# Guidance for OCR Twenty First Century Science - Controlled Assessed Investigation

I downloaded the OCR specimen task for the controlled assessed practical investigation. I did the task as if I were a student including writing it up; then I marked it as teacher. The pdf is an annotated version of my work, showing where I think I earned the marks.

Lots more guidance here: http://www.myphysics.org.uk/ks4cacswk.htm

Hope you find this useful.

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Motion of a Vehicle on a Surface
There are several factors that can affect the motion of a vehicle on a surface.
We need to consider the forces that are acting on the vehicle and the mass of the vehicle. It might be useful
to think about the momentum of the vehicle or to think about kinetic energy and work.
I am going to think about a vehicle that is coasting to a standstill (rather than one that is being pushed along by
a driving force). My vehicle will roll down a smooth ramp and then along a less smooth surface (such as
carpet).
Considering Factors
I could investigate what affects the distance it travels along the carpet. I could change the mass of the vehicle,
its start speed on the resistive surface itself.
Mass
If I increase the mass of the vehicle, then I'll increase its momentum and its kinetic energy. As force x time =
change in momentum, it should take longer to stop a vehicle that has got more momentum; if it takes longer
to stop, the vehicle should travel further. This also agrees with my common sense experience, pushing
shopping trolleys etc, the more loaded the trolley the further it goes if you get it going and let go of it.
Start Speed
If I increase the start speed of the vehicle, then it will have more momentum and more kinetic energy. In a
similar way to mass, more speed will mean a longer stopping distance. I know this also from riding my bike: if
I'm cycling fast, and have to stop suddenly I have a bigger braking distance the faster I'm going.
Surface
This will affect the size of the counter force. This is the force that slows a moving object down. On a rough
surface the wheels experience a force as they go over the bumps of the surface or as they push bits of the
surface out of the way. Pushing a wheel barrow over soft ground, the wheel sinks in a bit and is always
pushing mud out of its way. Marking: Good use of sci
terms ­ momentum, KE,
I've thought about the factors and I think I can do an interesting investigation: mass, etc. For Sa8
How does the start speed of a vehicle affect its distance to stop (when rolling over a rough
surface)?
Thinking about the kinetic energy of the vehicle, a higher speed means more kinetic energy KE= ½ m v2. So if
I double the speed of the vehicle, it will have four times the KE. As it rolls over the carpet a force will slow it
down. This force does work on the vehicle
Marking: Beginning of a quantitative prediction.
Work = Force x distance For Sa8
and the KE the vehicle had will equal the work done by the stopping force. I could assume that this force will
be the same whatever the speed. Then a vehicle with twice the speed would go four times the distance.
[20MINS]
I can illustrate this with some calculations.
Suppose I have two vehicles, both 0.4kg in mass. On leaves the slope at 3 m/s; the other one leaves the slope
at 6m/s.

## Other pages in this set

### Page 2

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KEslow = ½ m x v2 = 0.5 x 0.4 x 9 = 1.8 J
KEfast = ½ m x v2 = 0.5 x 0.4 x 36 = 7.…read more

### Page 3

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The spread of these results is from 0.105 to 0.107 ­ only 2 ms difference between the highest and the lowest
reading. This is much better than timing with a stopwatch. Timing 0.1 of a second with a stopwatch would not
be very reliable ­ human reaction time is not very consistent.
In the same check, I also measured the stopping distance of the trolley ten times. I measured this to the

### Page 4

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A184 Controlled Assessment Practical Investigation Mon YEAR
Name: Ally Davies Date: 23 May 2012
Title of activity: Motion of Vehicle on Slope
Hazards: Suggested Control Measures:
Slope could fall Hold in place with clamp
Trip hazard from equipment on floor / trailing leads Make sure all equipment is on desk or completely

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Controlling Risk
In this experiment there are few hazards and the risks they present are low. The board I am using as a ramp
might fall from its position. It is sensible to keep fingers and feet out of the gap under the ramp, just in case it
does slip, but it is not sharp on its edge and it is only raised by 25 cm at one end. It might hurt if it landed on

### Page 6

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Analysis
How stopping distance is affected by the start speed
110
100
90
Marking:
large scale axes
80 axes labelled with title and units
good for A6
Stopping Distance (cm)
70
60
50 Marking:
points accurately plotted
graph shows good line of best fit
40 good for A6
30
Marking: The spread of the data is clear because the graph shows
20 every data point that was recorded. The start speeds were almost the
same for each of the repeats, but not quite.…read more

### Page 7

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I collected data over a good range (ramp runs from 5 cm to 40 cm), but the speeds and the stopping distances
didn't actually change very much. I did 3 repeats for each ramp run length and I was careful to line everything
up so it was repeatable. I kept the ramp at 25.0cm height above the floor. I marked on the ramp the position
of the light gate, so I was sure it was in the same position every time.…read more