Question

Jogger runs 400 m East in 120 s, then turns around and runs 250 m West in 90 seconds. Calculate the following values.

Express your answer to 2 significant digits and include appropriate units. Show all your work.
(1 mark for work and 0.5 marks for correct answer to 2 significant digits)

a) speed

b) velocity

Answer 1

First, we must recall that distance is the total length traveled by an object in which the direction of the motion does not matter. Meanwhile, displacement is the distance of the object from its starting point which means the directions matters for displacement.

Now, speed is distance over time while velocity is displacement over time. Since we're talking about the same object's motion, the total time traveled is (120 + 90) = 210 seconds.

Now, the total distance traveled by the object is (400 + 250) = 650 m. Meanwhile the total displacement traveled by the object is 400 m, East + 250 m, West = 150 m, East.

Now, to find the speed and velocity, we just divide the values of distance and displacement, respectively, over time. Thus, we have

speed = 650 m / 210s ≈ 3.095 m/s
velocity = 150 m, East /210 s ≈ 0.714 m/s, East

Now, rounding the values up to 2 significant digits, we have

a) speed = 3.1 m/s
b) velocity = 0.71 m/s, East