TEST OF PRACTICAL KNOWLEDGE QUESTION You are... | WAEC SSCE - Physics - 2009

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TEST OF PRACTICAL KNOWLEDGE QUESTION

You are provided with two meter rules and other necessary apparatus.
Place one of the rules on a knife edge and determine its centre of gravity C. Mark this pos with a piece of chalk.
Read and record the mass M\(_{R}\) of the metre rule written on the reverse side of it.
Attach the mass M= 100g firmly to the rule AB at C using sellotape.
Suspend the metre rule by two parallel threads of length h = 40 cm each at the 10 cm marks. Ensure that the graduated face to the metre rule is facing upwards.
Set the rule AB into a small angular oscillation about the vertical axis through its centre of gravity.
Determine the time, t for 20 complete oscillations. Evaluate the period T and T\(^{2}\)
Read and record the value of d in meters.
Keeping d constant throughout the experiment, repeat the procedure for other values of h = 50, 60, 70, and 80 cm. In each case determine the corresponding values of f T and T. Tabulate your reading. (x) Plot a graph of T on the vertical axis and h on the horizontal axis.
Determine the slope S, of the graph. Evaluate k =s, where Q =2 S, Q 250P
State two precautions taken to ensure accurate results.

(b)i. Define the term couple as it relates to rotational or oscillatory systems.

ii. Give two practical application of a couple in everyday life.

Answer

Answer Details

(a) The torsional-oscillation experiment (metre rule as a bifilar/torsional pendulum)

The graduated metre rule is balanced on a knife edge to locate its centre of gravity \(C\) (this is the theory the experiment relies on). A \(100\ \text{g}\) mass is fixed at \(C\), and the rule is suspended horizontally by two vertical threads of equal length \(h\), a distance \(d\) apart, attached symmetrically about \(C\). When the rule is given a small twist about the vertical axis through \(C\), it performs simple angular (torsional) oscillations. The period is timed for 20 oscillations, giving \(T = \dfrac{t}{20}\), and \(T^{2}\) is evaluated. The procedure is repeated for \(h = 40, 50, 60, 70, 80\ \text{cm}\) at fixed \(d\), and a graph is plotted.

Two precautions:

Ensure the two suspension threads are of exactly equal length and are vertical and parallel, so the rule hangs horizontally.
Give only a small angular displacement (small twist) so the oscillations remain simple harmonic, and time a large number (20) of complete oscillations to reduce timing/reaction-time error, avoiding sideways swinging.

(b)(i) Couple

A couple is a pair of equal, parallel and opposite forces whose lines of action do not coincide. A couple produces (or tends to produce) rotation only, not translation. The turning effect (moment/torque) of a couple is:

\[ \text{Torque} = \text{one force} \times \text{perpendicular distance between the forces} = F\times d \]

(b)(ii) Two practical applications of a couple:

Turning a steering wheel of a vehicle with both hands.
Winding a clock, opening a water tap, or turning a screwdriver / the two hands opening a corkscrew.

Read lesson note on Equilibrium Of Forces (WAEC)

Equilibrium Of Forces

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TEST OF PRACTICAL KNOWLEDGE QUESTION You are provided with two meter rules and other necessary apparatus. Place one of the rules on a knife edge and determi...

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TEST OF PRACTICAL KNOWLEDGE QUESTION You are provided with two meter rules and other necessary apparatus. Place one of the rules on a knife edge and determi...

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