Question

Using a starting position p, a speed s, and a time t, write two expressions for an ending position. One expression should show the result of moving right, and one expression should show the result of moving left.

going right:

going left:

Answer 1

Explanation:

We can use signed numbers to represent the position of an object along a line. We pick a point to be the reference point, and call it zero. Positions to the right of zero are positive. Positions to the left of zero are negative.

When we combine speed with direction indicated by the sign of the number, it is called velocity. For example, if you are moving 5 meters per second to the right, then your velocity is +5 meters per second. If you are moving 5 meters per second to the left, then your velocity is -5 meters per second.

If you start at zero and move 5 meters per second for 10 seconds, you will be 5⋅10=50 meters to the right of zero. In other words, 5⋅10=50 .

If you start at zero and move -5 meters per second for 10 seconds, you will be 5⋅10=50 meters to the left of zero. In other words,

−5⋅10=−50

In general, a negative number times a positive number is a negative number.