Distance, Speed & Time (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note

Planes fly at typical speeds of around 250 m/s. Calculate the distance travelled by a plane moving at this speed for 2 hours.

Answer:

Step 1: List the known quantities

• Speed, v = 250 m/s

• Time, t = 2 hours

Step 2: Write the relevant equation

v = $\frac{s}{t}$

Step 3: Rearrange for distance travelled, s

s = v × t

Step 4: Convert any units

• The time given in the question is not in standard units

• Convert 2 hours into seconds:

2 hours = 2 × 60 ×60 = 7200 s

Step 5: Substitute in the values for speed and time

s = 250 × 7200 = 1 800 000 m

Florence Griffith Joyner set the women’s 100 m world record in 1988, with a time of 10.49 s. Calculate her average speed during the race. 

Answer:

Step 1: List the known quantities

• Distance, s = 100 m

• Time, t = 10.49 s

Step 2: Write the relevant equation

• Sprinters typically speed up out of the blocks up to some maximum speed

• Because Florence’s speed changes over the race, we can calculate her average speed using the equation:

average speed = $\frac{\mathrm{distance}\mathrm{travelled}}{\mathrm{time}\mathrm{taken}}$

Step 3: Check any unit conversions

• Check that all quantities given in the question are in standard units

• In this example, they are all in standard units

Step 4: Substitute the values for total distance and time

average speed = $\frac{100}{10.49}$

average speed = 9.53288... = 9.53 m/s