A-LevelPhysicsForces, density and pressure9702/32 · May/June 2019 · Q220 Marks

In this experiment, you will investigate the friction between an inclined board and a wooden block.

(a)• Set up the apparatus as shown in Fig. 2.1. • Adjust the apparatus until the angle θ between the board and the bench has a value between 32° and 38°. • Measure and record θ. θ = .°[1]
(b)• Attach the newton meter to the wooden block using the string loop. • Place the block on the board, with the label of the block at the top. • Pull the newton meter and block up the board at a constant speed. Keep the string loop parallel to the board, as shown in Fig. 2.2. • Record the force F when the block is travelling at a constant speed. F= [2]
(c)Estimate the percentage uncertainty in your value of F. percentage uncertainty = [1]
(d)(i)• Adjust the board so that θ is between 12° and 18°. • Measure and record θ. θ = .°[1]
(d)(ii)Repeat (b). F= [2]
(e)Using the newton meter, measure and record the weight W of the block and hook. W = [1]
(f)(i)It is suggested that the relationship between F, W and θ is F/W = sin θ + μcos θ where μ is a constant. Using your data, calculate two values of μ. first value of μ = second value of μ = [1]
(f)(ii)Explain whether your results support the suggested relationship.[1]
(g)Using your second value of μ, calculate the value of F when θ = 65°. Give your answer to an appropriate number of significant figures. F= [2]
(h)(i)Describe four sources of uncertainty or limitations of the procedure for this experiment. 1. 2. 3. 4.[4]
(h)(ii)Describe four improvements that could be made to this experiment. You may suggest the use of other apparatus or different procedures. 1. 2. 3. 4.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

[1] Value for θ recorded to nearest degree and θ < 90°.
[1] Value for F recorded to nearest 0.1 N with unit.
[1] Evidence of repeat readings of F.
[1] Percentage uncertainty in F based on an absolute uncertainty of 0.2–0.5 N. If repeated readings have been taken, then the uncertainty can be half the range (but not zero) if the working is clearly shown. Correct method of calculation to obtain percentage uncertainty.
[1] Second value for θ.
[1] Second value for F.
[1] Quality: Second F < first F.
[1] Value of W in range 1.0–5.0 N with unit.
[1] Two values of μ calculated correctly.
[1] Valid comment consistent with the calculated values of μ, testing against a criterion specified by the candidate.
[1] Correct calculation of F.
[1] F given to 2 or 3 significant figures.
[1] Two readings are not enough to draw a (valid) conclusion (not "not enough for accurate results", "few readings").
[1] Difficult to clamp board so that it is stable.
[1] Difficult to pull (block) at steady speed.
[1] Difficulty with F/force/newton-meter reading with reason (e.g. fluctuates / friction varies in different places).
[1] F is small so percentage uncertainty in F is large.
[1] Take more readings and plot a graph or take more readings and compare μ values (not "repeat readings" on its own).
[1] Improved clamping method e.g. use two clamps/fix base to bench with adhesive putty.
[1] Detail of constant speed pulling arrangement (e.g. use motor/pulley with mass adjusted to give terminal velocity).
[1] Video/film/record linked to measurement of force.
[1] Use force sensor with data logger/use more precise newton-meter/add masses on top of block.