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Set 1 Problem number 5


Problem

At the rate 6 meters per second, how long does it take to move 2.4 meters?

Solution

At 6 meters every second, it will clearly take less than a second to move 2.4 meters.

The ratio of displacement to displacement in a second is 2.4/ 6 = .4, so the time interval is .4 second.

Generalized Solution

Generalized Response: We can obviously rearrange

`ds = vAve `dt

into the form

`dt = `ds / vAve.

This form represents the ratio `ds / vAve of the displacement moved to the displacement moved in a second.

If, as in the present problem, the numerical value of `ds is less than that of v, this means that we have moved less displacement than would be moved in a second. So the time interval `dt is less than a second.

The smaller the ratio `ds / vAve, the less the time required.

Explanation in terms of Figure(s), Extension

We can reason out the result, as above. As an alternative, the figure below shows the diagram in the form of a 'relationship triangle' between `ds, `dt and vAve, showing how we can use the known quantities `ds and vAve to find the time interval `dt.

Figure(s)

the_v_ds_dt_triangle.gif (3046 bytes)

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