Speed, Distance, and Time
--Q-Type#1: Calculating average speed--
Average speed (mph) = Total Distance (m)/Total time (h)
Total distance = speed x mins/60
Part 1: 12mph x 1/6 (10 mins = 1/6 of an hour) = 2 miles
Part 2: 20mph x 1/4 (15 mins = 1/4 of an hour) = 5 miles
Total time = 1/6 of an hour + 1/4 an hour = 5/12 of an hour
7/(5/12 of an hour) = 16.8mph
--Q-Type#2: Passing from opposite direction--
"When you have two objects speeding towards each other, the speeds are added; for example, if a car is travelling at 80 km/h towards another at 70 km/h, then the 'relative speed' is 80+70 = 150 km/h; therefore, to work out 'How long (in hours) before they collide?' You should "divide the distance apart by this relative speed."
"So, they will meet after 120/150 of an hour, which is 0.8 of an hour = 48 minutes."
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--Q-Type#3: Catching up in same direction--
"When you have two objects leaving at different times with the slower object leaving first and you wish to work out when the faster one overtakes, the 'relative speed' is = faster speed − slower speed, for example
Time to meet = distance apart ÷ relative speed
"Now let's try some harder questions. Follow the logical steps below to work out the answer."
Density = Mass/Volume
Mass = Density x Volume
Volume
