Rates Flashcards
What is a rate?
Distance/time
Distance=
Rate x time
Time=
Distance/rate
Average rate =
Total distance / total time
What is important to know about converging rage problems (when two objects are moving towards each other)?
The total distance will be equal to the sum of the individual distances each object travels.
When two objects leave at the same time of day and converge at a constant rate, what must be true?
They will have travelled for the same time at the instant that they meet.
When one object is travel faster than another object, what should you consider doing in the matrix approach?
Consider setting the slower object’s speed to be some variable (r) and the faster object’s speed to be r + the difference in speeds.
When two objects leave at different times and converge at a constant rate, how do you represent time?
The travel time of the object that leaves later can be represented by some variable t and the travel time of the object that leaves earlier can be represented by t+ the difference between their departure times.
In a diverging rate question, what must be true?
The sum of the distances that the two objects travel must equal the total distance travelled between the two objects.
What must be true in a round trip problem?
The distance an object travels from the starting point to the destination equals the distance the object travels back from the destination to the starting point.
What should you consider when only the total time is provided in a round-trip question?
Consider letting the time to a destination equal some variable t and the time back equal (total trip time - t)
What’s the rule for catch up questions?
When two objects start from the same point and catch up to each other, both objects will have travelled the same distance when they meet.
What is the shortcut for catch up and pass problems?
Time = change in distance / change in rate
Don’t use this for catch up questions (because the distances are equal there is no changes in them)
What must you know about catch up and pass questions?
The faster object’s distance is equal to the slower object’s distance plus any difference in starting points and any distance by which the faster object must pass the slower object.
What is the formula for work?
Rate x time
