5.17 Required practical: acceleration
9 exam questions worth 25 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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State the independent variable, the dependent variable and one control variable in Part A of this investigation.
Mark scheme
independent: the force (hanging mass) (1); dependent: acceleration (1); control: total mass of the system (1)
Model answer
The independent variable is the force. The dependent variable is the acceleration. The total mass is a control variable.
In Part A, a student moves masses from the trolley to the hanger, rather than adding new masses to the hanger. Explain why.
Mark scheme
so that the total mass of the system stays the same (1); so only the force changes / mass does not affect the results (1)
Model answer
This keeps the total mass of the system constant, so only the force changes.
A mass of 0.050 kg hangs from the string. Calculate the force that accelerates the trolley. (g = 9.8 N/kg)
Mark scheme
F = m g = 0.050 × 9.8 (1); 0.49 N (1)
Model answer
F = m g = 0.050 × 9.8 = 0.49 N.
The trolley's velocity is 0.20 m/s at the first light gate and 0.80 m/s at the second, 1.5 s later. Calculate its acceleration.
Mark scheme
a = (v − u) ÷ t (1); (0.80 − 0.20) ÷ 1.5 (1); 0.40 m/s² (1)
Model answer
a = (v − u) / t = (0.80 − 0.20) / 1.5 = 0.40 m/s².
A graph of acceleration against force for a constant mass is a straight line through the origin. State what this shows and what the gradient of the line is equal to.
Mark scheme
acceleration is directly proportional to force (1); the gradient is 1 ÷ mass (1)
Model answer
Acceleration is directly proportional to force. The gradient equals 1/mass.
The line on the graph does not pass through the origin, but crosses the force axis at a small positive value. Suggest a reason and explain the effect.
Mark scheme
friction acts (1); so some of the force is needed to overcome friction before the trolley accelerates (1)
Model answer
Friction opposes the motion, so some of the force is needed to overcome it before the trolley can accelerate.
Describe how the apparatus can be adjusted to compensate for friction.
Mark scheme
raise the end of the runway at the start slightly (so the trolley slopes down) (1); until the trolley moves at a constant speed when given a small push / when there is no hanging mass (1)
Model answer
Raise the start of the runway slightly until the trolley moves at a steady speed when pushed gently, with no hanging mass.
Explain two precautions that should be taken to make the results more accurate.
Mark scheme
string parallel to the bench (1); so the whole weight acts along the direction of motion (1); repeat the readings and calculate a mean (1); to reduce the effect of random errors (1)
Model answer
Make sure the string is parallel to the runway, so the full weight pulls the trolley. Repeat each reading and find a mean to reduce random errors.
Describe a method to investigate how the acceleration of a trolley depends on its mass, when the resultant force is kept constant.
Mark scheme
keep the hanging mass the same so the force is constant (1); measure the mass of the trolley (1); release the trolley and measure acceleration using light gates / data logger (1); add masses to the trolley and repeat (1); plot acceleration against mass (or 1 / mass) (1)
Model answer
Hang a constant mass, such as 50 g, from the string, so the force is constant. Measure the mass of the trolley, release it, and use light gates and a data logger to measure its acceleration. Add masses to the trolley one at a time, repeat, and plot acceleration against mass.
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