Sec 3 Combined Science (Physics) Measurement topical questions

State the SI base quantity measured by each unit: (a) kilogram, (b) second, (c) ampere.

Convert (a) 250 cm to m and (b) 3.5 kg to g.

Classify each as scalar or vector: energy, force, time, velocity.

State what is meant by the range of an instrument, and what happens if the range is too small.

A laboratory balance reads to 0.01 g and a kitchen balance to 1 g. Explain which to use for measuring 0.15 g of a powder, and state one thing the better balance cannot do.

Convert (a) 620 nm to m and (b) 8.2 GW to W, giving each answer in standard form.

A student measures the width of a book with a rule as 21.4 cm. (a) State the precision of the rule. (b) Explain why "21.4000 cm" is not a better answer. (c) The book's thickness is best measured as 3.2 cm with the same rule. Suggest why the last digit is less reliable.

Three labelled bottles hold lengths of 2 × 10⁻⁹ m, 2 × 10⁻⁴ m and 2 × 10⁷ m. Match each bottle to the most likely object: the Earth's diameter, a molecule, the width of a human hair. Justify each match with one order-of-magnitude sentence.

A tugboat pulls a ship with 80 000 N forwards while the water drags back with 65 000 N. (a) State the size and direction of the resultant force. (b) The tug doubles its force; state and explain the new resultant. (c) State whether the water drag is a scalar or a vector and why.

A student must measure (a) the time for 20 swings of a pendulum, (b) the volume of a small stone, and (c) whether two rods differ in length by less than 1 mm. For each, choose suitable instruments and justify with range and precision.

A train travels 40 km east, then 40 km west, in a total of 1.0 hour. (a) Calculate its average speed. (b) State its average velocity. (c) Explain why the two differ.

A sensitive electronic thermometer reads to 0.01 °C, and a mercury thermometer to 0.5 °C. (a) Which should track the temperature of a water bath rising towards 90 °C, and why does the electronic one still need a range check? (b) A student argues the 0.01 °C thermometer is therefore always better. Give one situation where the mercury thermometer is the better choice, with a reason.