Independent assessment practice

A 40 kg delivery robot moves up a ramp. Along the ramp, its motors provide 260 N uphill, while friction and rolling resistance together provide 60 N downhill. The component of its weight down the ramp is 120 N.

1. a

   Represent Describe a correct free-body diagram for the robot.

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   1. 1

      Includes the 260 N driving force uphill and the 60 N resistance downhill.

   2. 2

      Includes weight vertically downward and a normal contact force perpendicular to the ramp.

   3. 3

      Does not add a separate ‘force of motion’ or treat the 120 N component as an extra force in addition to weight.

2. b

   Calculate Calculate the resultant force parallel to the ramp and the robot's acceleration.

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   1. 1

      Calculates resultant = 260 − 60 − 120 = 80 N uphill.

   2. 2

      Uses a = F ÷ m.

   3. 3

      Obtains a = 80 ÷ 40 = 2.0 m s⁻² uphill.

3. c

   Predict Predict the motion if the driving force falls to 150 N while the other forces are unchanged.

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   1. 1

      The resultant is 30 N downhill, so an upward-moving robot slows; it would later accelerate downhill if the forces remained unchanged.

Students change the frequency of a wave generator on the same stretched cord. They measure wavelength and calculate wave speed.

1. a

   Verify Verify the calculated speed for the 10.0 Hz reading.

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   1. 1

      Uses v = fλ.

   2. 2

      Calculates v = 10.0 × 1.18 = 11.8 m s⁻¹.

2. b

   Identify Identify the anomalous row and justify your decision quantitatively.

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   1. 1

      Identifies the 12.5 Hz row.

   2. 2

      States that its calculated speed is 15.0 m s⁻¹ while the other results cluster around 12.0 m s⁻¹.

   3. 3

      Quantifies the difference, for example 3.0 m s⁻¹ or about 25% above 12.0 m s⁻¹.

3. c

   Evaluate Evaluate the conclusion that frequency changes wave speed on this cord.

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   1. 1

      States that the non-anomalous data support approximately constant speed as frequency changes.

   2. 2

      Explains that wavelength decreases as frequency increases so fλ remains nearly constant.

   3. 3

      Suggests repeating the anomalous measurement and controlling tension, because tension or measurement error could explain the difference.

A school has a sealed low-activity source, a radiation detector, a stand, and equal-area sheets of paper, aluminium, and acrylic. Under approved supervision, students want to compare how the materials affect count rate. They must not handle the source directly.

1. a

   Formulate Write a focused research question and identify the independent and dependent variables.

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   1. 1

      Writes a question comparing absorber material or controlled absorber thickness with corrected count rate.

   2. 2

      Identifies absorber material or thickness as the independent variable.

   3. 3

      Identifies background-corrected count rate as the dependent variable.

2. b

   Design Describe a safe method that produces reliable, comparable data.

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   1. 1

      Measures background for a sufficiently long fixed interval and subtracts it from each source-plus-background result.

   2. 2

      Keeps source–detector distance, alignment, counting time, absorber area, and detector settings constant.

   3. 3

      Repeats each condition in a varied or randomised order and calculates means with spread or uncertainty.

   4. 4

      Uses the stand or tongs and follows local source rules to minimise time near the source, maximise distance when possible, and avoid direct handling.

3. c

   Evaluate Explain why a result with aluminium lower than paper does not by itself identify the radiation or prove aluminium is always the best shield.

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   1. 1

      Explains that source emission may be mixed and attenuation also depends on absorber thickness or mass per area, geometry, and detector response.

   2. 2

      Explains that shielding choice also depends on radiation type, secondary radiation, required reduction, practicality, and safety context; one comparison cannot support a universal claim.