1. A. 2.40x103 km min-1, B. 6.67x10-1 km min-1 C. 1.50 km min-1
QUESTION:
A car is traveling at a speed of 40.0 km hr-1. How fast is the car moving in km min-1?
A. 2.40x103 km min-1, B. 6.67x10-1 km min-1 C km min-1
A car is traveling at a speed of 40.0 kilometers per hour. How fast is the car moving in kilometers per minute?
PAUSE CLICK CONTINUED ON NEXT SLIDE

2. A. 2.40x103 km min-1, B. 6.67x10-1 km min-1 C. 1.50 km min-1
QUESTION:
A car is traveling at a speed of 40.0 km hr-1. How fast is the car moving in km min-1?
A. 2.40x103 km min-1, B. 6.67x10-1 km min-1 C km min-1
1 hr
40.0 km x
= km min-1
6.67x10-1 km min-1
or 6.67x10-1 km/min
60 min hr
In this problem, we are asked to change the time unit from hour to minutes.
So the possible conversion factors that we can use are
HIGHLIGHT 1 hr/60 min
1 hour over 6o minutes,... or
HIGHLIGHT 60 min/1 hr
60 minutes over 1 hour...
Let’s see which one we need to use.
First, we write the known amount kilometers
CLICK per hour....
CLICK CLICK Note that raising a quantity to a –1 power, is the same thing as putting it in reciprocal form.
That is, hour to the negative 1 power, means that the hour unit is the denominator.
Since we want to replace hour by minute, we use the conversion factor that will allow
us to cancel the hour unit. Therefore , we use this conversion factor....
HIGHLIGHT 1 hr / 60 min
We multiply our known amount...
CLICK
by 1 hour
over
CLICK 60 minutes
The hour unit cancels.
SHOW CANCELLATION OF hr units
This gives us an answer of kilometers per minute, which
we need to round off the three significant digits.
HIGHLIGHT 6.67x10-1 km min-1.
since our original quantity, 40.0 kilometers per hour, has 3 significant digits.
Therefore, the correct answer is B.
Note that instead of raising the unit to a –1 power, we can instead put a slash in front of it.
HIGHLIGHT slash in 6.67x10-1 km/min
PAUSE END RECORDING
1 hr
60 min
60 min
1 hr

3. Video ID: 1A-5-4 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08