In this experiment, you will investigate the motion of a swinging bob and a wooden rod. (a) Measure and record the distance $L$ between the end of the rod and the end of the hook as shown in Fig. 1.1. $L$ = \_\_\_\_\_\_ $\text{m}$ (i) Set up the apparatus as shown in Fig. 1.2. The distance between the bottom of the split cork and the centre of the bob should be equal to the value of $L$ in (a). (ii) Reduce the distance between the bottom of the split cork and the centre of…

Physics 9702/35 — October/November 2013

Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme

questions

marks

120

minutes

Topics Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation

Q1Manipulation, Measurement and ObservationPresentation of Data and ObservationsAnalysis, Conclusions and EvaluationFree sample

In this experiment, you will investigate the motion of a swinging bob and a wooden rod.

(a)

Measure and record the distance $L$ between the end of the rod and the end of the hook as shown in Fig. 1.1.

Fig. 1.1

$L$ = ______ $\text{m}$

(b)

(i)

Set up the apparatus as shown in Fig. 1.2.

Fig. 1.2

The distance between the bottom of the split cork and the centre of the bob should be equal to the value of $L$ in (a).

(ii)

Reduce the distance between the bottom of the split cork and the centre of the bob by approximately $3\ \text{cm}$ .

(iii)

Measure and record the distance $D$ between the bottom of the split cork and the centre of the bob, as shown in Fig. 1.3.

Fig. 1.3

$D$ = ______ $\text{m}$

(iv)

Calculate $x$ where $x = L - D$ .

$x$ = ______ $\text{m}$

(c)

(i)

Move the bob towards you.
Release the bob and watch the movement.
The bob will move away from you and back towards you, completing a swing.

(ii)

Move the bottom of the wooden rod towards you.
Release the rod and watch the movement.
The rod will move away from you and back towards you, completing a swing.

(iii)

Move the bob and the bottom of the rod towards you.
Release the bob and the rod at the same instant and watch the movement.
The bob and the rod will swing backwards and forwards becoming out of step.
Eventually they will, for a short time, move together in step.

(iv)

Repeat (iii) and count the number $n$ of swings of the bob between releasing the bob and rod and when they are back in step. Record $n$ .

$n$ = ______

(d)

Decrease $D$ and repeat (b)(iii), (b)(iv) and (c)(iv) until you have six sets of values of $D$ , $x$ and $n$ .
Your values of $D$ should be in the range $D \geq 40\ \text{cm}$ .
Include values of $\left( \frac{n + 1}{n} \right)^2$ in your table.

10M

(e)

(i)

Plot a graph of $\left( \frac{n + 1}{n} \right)^2$ on the $y$ -axis against $x$ on the $x$ -axis.

(ii)

Draw the straight line of best fit.

(iii)

Determine the gradient and $y$ -intercept of this line.

gradient = ______
$y$ -intercept = ______

(f)

The quantities $n$ and $x$ are related by the equation

\left( \frac{n + 1}{n} \right)^2 = - Px + Q

where $P$ and $Q$ are constants.

Use your answers in (e)(iii) to determine the values of $P$ and $Q$ .
Give appropriate units.

$P$ = ______
$Q$ = ______

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