A car drives at 81 km/h. A clap of thunder travels at 330 m/s…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A car drives at . A clap of thunder travels at .
- What is the car's speed in metres per second?
- What is the speed of the sound in kilometres per hour?
Need a reminder? The key ideaShow
To change a unit, multiply by a fraction that equals one, such as , so that the old unit cancels. A prefix goes with the unit's power:
: km/h to m/s, divide by ; m/s to km/h, multiply by .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Car. .
Step 2. Sound. .
Answer: (a) . (b) .
Check. Sound is about times faster than the car either way: and .
Watch out. A metre per second is the bigger unit, so a speed in m/s is the smaller number.
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