# 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.

Excellent preparation for your actual controlled assessed coursework task for Additional Science of Physics GCSE.

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

Hope you find this useful.

- Created by: allydavies
- Created on: 11-06-12 20:16

First 576 words of the document:

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.

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