D = rt
Uniform Motion
Three types of problems:
- Motion in opposite direction
- Motion in same direction
- Round Trip
Motion in opposite direction
For this we used different students bicycling ... Jeff K and Jeff B in 5th period and Rebecca and Cayla from 6th period.
Last year's examples follow:
They start at noon --60 km apart riding toward each other. They meet at 1:30 PM. If Josh K speed is 4 km/h faster than Josh P ( Maddie is greater by the same from Jamie's rate) What are their speeds?
We set up a chart
Motion in Same Direction
Next we had a fictitious story about Stan's Helicopter and Brett's plane ( or David's helicopter and Noah's Smiling Plane) taking off from Camarillo Airport flying north. The helicopter flies at a speed of 180 mi/hr. 20 minutes later the plane takes off in the same direction going 330 mi/hr. How long will it take Brett (or Noah) to over take Stan's ( or David's) helicopter?
Let t = plane's flying time
Make sure to convert the 20 minutes ---> 1/3 hours.
We set up a chart .. Here is the chart with last year's names:
When the plane over takes the helicopter they have traveled the exact same distance so set them equal
180(t + 1/3) = 330t
180 t + 60 = 330t
60 = 150t
t = 2/5
which means 2/5 hour. or 24 minutes.
Round Trip
A ski lift carries Sammy ( or Jessica) up the slope at 6 km/h Sammy or Jessica snowboard down 34 km/h. The round trip takes 30 minutes.
Did you see the picture?
Let t = time down
then set up a chart
6(.5 -t) = 34 t
3 - 6t = 34 t
3/40 = t
Now, what's that?
0.75 hr or 4.5 minutes
How far did they snowboard... plug it in
34(0.075) = 2.55 km
No comments:
Post a Comment