Q4CQ - College Physics (Urone)

Question

A student writes, “A bird that is diving for prey has a speed of $\mathbf{-}\mathbf{10}\mathbf{\text{\hspace{0.17em}m/s}}$.” What is wrong with the student’s statement? What has the student actually described? Explain.

Step-by-Step Solution

Answer

The student has described the speed. The velocity of the bird should be given if the direction is mentioned then.

Step 1: Speed and Velocity

Speed: It is defined as the ratio of the distance traveled by the body per the amount of time taken to travel that distance.

The speed is always mentioned in the SI unit of meter/ Second.

Speed is considered a vector quantity. Hence it requires only the magnitude to mention speed. Direction is not necessary.

Velocity: Velocity is the ratio of displacement of the body to the time taken to complete that displacement. 

Velocity is a vector quantity. It is very necessary to show magnitude and direction with the magnitude. It also has the same SI unit, but the direction is necessary.

Step 2: Correct Statement

 In the above statement, “A bird that is diving for prey has a speed of  $\mathbf{-}\mathbf{10}\mathbf{\text{\hspace{0.17em}m/s}}$”, the negative sign represents the direction of the bird's velocity. Hence if the quantity has both magnitude and direction, it is considered a vector quantity.

In that case, the correct statement should be, A bird diving for prey has a Velocity of $\mathbf{-}\mathbf{10}\mathbf{\text{\hspace{0.17em}m/s}}$ .

Therefore, it is concluded that the student should have used velocity instead of speed in the statement.