Question

An object starts at a point +15m goes 20m toward +X direction in 4s then suddenly changes its direction to the opposite and covers 45m in 5s.

A. Where is the object after the first 4s (position)?
B. What total distance did it travel?
C. What was its total displacement?
D. What was its average velocity for the entire trip?

Answer 1

We want to study the one-dimensional movement of a given object.

A) 35m

B) 65m

C) 25m

D) 2.78 m/s

First, let's write the given positions of the object.

We know that the object starts at the point 15m, then at t = 0s we have:

(0s, 15m)

Then it moves 20m towards +x in 4 seconds, so the new position is:

(4s, 35m).

Finally, it changes of direction and moves 45m in 5 seconds, then the final position is:

(9s, -10m).

A) We already know the position after 4 seconds, is 35m in the positive x-axis.

B) The total distance traveled is:

20m + 45m = 65m

C) The displacement is given by the distance between the final position (-10m) and the initial position (15m) we will get:

|-10m - 15m| = 25m

The displacement is equal to 25m

D) The average velocity can be computed as the quotient between the displacement (with the correspondent sign, in this case negative) and the time it takes to travel it.

We have:

AV  = -25m/9s = 2.78 m/s.

The negative sign is because the object moves to the left.

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