In this experiment, you will measure the average speed of a toy car moving across a bench. You pushes the car so that it rolls from one end of the bench tow...
Question 1 Report
In this experiment, you will measure the average speed of a toy car moving across a bench. You pushes the car so that it rolls from one end of the bench towards the other. You places two markers A and B on the bench. You uses a stopwatch to time the car as it travels from marker A to marker B. Fig. 7.1 shows the arrangement. The distance between the markers is shown on the centimetre scale below the bench. The stopwatch reading is shown.
(a) Measure the distance between markers A and B from the scale in Fig. 7.1. [1]
(b) Record the time from the stopwatch reading in Fig. 7.1. [1]
(c) Calculate the average speed of the car between the two markers. Show your working and give the unit. [1]
(d) Explain why the speed you calculated is an average speed and not the actual speed at every point. [1]
(e) Describe how you could obtain a more accurate time measurement using the same markers. [1]
(f) Give one source of error when using a stopwatch for this measurement. [1]
(g) Write the equation that relates average speed, distance and time. [1]
Answer Details
(a) From the centimetre scale in Fig. 7.1, marker A is at 0 cm and marker B is at 80 cm. [1]
\[ \text{Distance} = 80.0 \text{ cm} \]
(b) From the stopwatch display: [1]
\[ \text{Time} = 1.65 \text{ s} \]
(c) [1]
\[ \text{Average speed} = \frac{\text{distance}}{\text{time}} = \frac{80.0 \text{ cm}}{1.65 \text{ s}} = 48.5 \text{ cm/s} \]
Equivalently, \( 0.800 \div 1.65 = 0.485 \text{ m/s} \). Either unit is acceptable provided the working is consistent.
(d) This is an average speed because it equals the total distance divided by the total time for the whole journey. The car may speed up or slow down between A and B due to friction or the initial push. The calculated value does not represent the instantaneous speed at any single point along the path. [1]
(e) Use a light gate at each marker connected to an electronic timer. The light gates trigger automatically as the car passes, removing human reaction time delay and giving a more precise measurement. Alternatively, repeat the measurement several times and calculate a mean time. [1]
(f) Human reaction time introduces error when starting and stopping the stopwatch. There is a delay between seeing the car cross a marker and pressing the button, and this delay may differ at the start and end, leading to an inaccurate time reading. [1]
(g) [1]
\[ \text{average speed} = \frac{\text{distance}}{\text{time}} \]
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