Sec 3 Physics Physical Quantities & Measurement topical questions

Complete the table of base quantities and units.

Convert each measurement as instructed.

1. (a)2.6 GHz into hertz[1]
2. (b)780 nm into metres[1]
3. (c)0.84 km into metres[1]

State whether each quantity is a scalar or a vector: energy, weight, density, acceleration.

A student measures a liquid volume in a measuring cylinder. Describe how she should read the scale to avoid the two main reading errors.

A micrometer screw gauge reads 0.03 mm with its jaws closed. A student uses it to measure the diameter of a wire four times: 0.52 mm, 0.53 mm, 0.52 mm and 0.66 mm.

1. (a)Name the type of error shown by the closed-jaw reading.[1]
2. (b)Explain which reading should be excluded before averaging.[2]
3. (c)Calculate the corrected average diameter of the wire.[2]

A ticker-tape timer marks 50 dots per second. A student states "the timer measures time to 1/50 s, so it is more precise than any stopwatch".

1. (a)State the time interval between neighbouring dots.[1]
2. (b)Give one reason why a ticker-timer measurement of a very short interval can still be imprecise.[1]
3. (c)A pendulum has a period of about 0.80 s. Describe how to measure its period as precisely as possible with a stopwatch.[2]

The Sun is about 1.5 × 10¹¹ m from the Earth and a gold atom is about 3 × 10⁻¹⁰ m in diameter.

1. (a)Estimate how many gold atoms, laid side by side, would span the Earth–Sun distance. Give your answer to 1 significant figure.[2]
2. (b)State the orders of magnitude of both distances.[2]

A spring balance reads 0.2 N with no load hanging from it.

1. (a)State the name of this error and its effect on every reading taken with the balance.[2]
2. (b)A bag of sugar is hung on the balance, which reads 10.7 N. State the corrected weight of the sugar.[1]
3. (c)The balance has divisions every 0.2 N. Explain whether it is suitable for finding the weight of a single 2 g coin, taking g = 10 N/kg.[2]

Two tugs pull a ship. One pulls with 25 kN due north; the other with 32 kN due east.

1. (a)Draw a labelled scale vector diagram of the two forces and the resultant (state your scale).[2]
2. (b)From the diagram (or by calculation as a check), find the magnitude of the resultant pull.[2]
3. (c)State the direction of the resultant as an angle.[1]

A car park barrier gate is 4.2 m long and a student's thumb is about 12 mm wide.

1. (a)Estimate the order of magnitude of the ratio (gate length ÷ thumb width).[2]
2. (b)Explain why the exact ratio is not physically interesting here.[1]

A kite is held by two strings making equal angles. One string pulls with a tension of 1.2 N towards 40° north of east; the other pulls with 1.2 N towards 40° south of east (the two tensions are 80° apart).

1. (a)Without drawing, state the bounds within which the resultant of the two tensions must lie.[2]
2. (b)Using a scale diagram (or a calculation as a check), find the approximate magnitude and direction of the resultant force.[4]

The period T of a pendulum was measured for five different lengths with the many-oscillations method. The data is plotted with T² on the y-axis and length L on the x-axis, giving a straight line through the origin with gradient 4.0 s²/m.

1. (a)Explain why timing 20 oscillations, rather than 1, improves the measurement, and why the timing starts at the centre of the swing.[3]
2. (b)Use the gradient to determine g, given T² = (4π²/g) L.[2]
3. (c)The true value of g in Singapore is about 9.78 m/s². Calculate the percentage difference from the value in (b).[1]

A student wants the density of a rectangular metal block. She has a metre rule (1 mm), an electronic balance (0.01 g) and the block: length 10.0 cm, width 3.0 cm, height 2.0 cm, mass 163.0 g.

1. (a)Calculate the density in g/cm³ and then in kg/m³.[3]
2. (b)The balance is precise to 0.01 g but the rule only to 1 mm (0.1 cm). Explain which measurement limits the precision of the density.[2]
3. (c)Suggest one improvement to the length measurement that increases its precision without changing instruments.[1]