Question

Can the speed of a body be negative?

Answer 1

Hint: Speed is a scalar quantity and the scalar quantity are quantities which are having only magnitude, the scalar quantities do not have the direction. So, when there is no mention of the direction of a given quantity then the chances of that quantity to be negative is likely to be impossible.

Complete answer:
The speed of a body can never be zero and this can be justified with the help of the two reason:
One reason is that it is a scalar quantity and scalar quantity cannot be negative, and the explanation is done in the hint.
Second reason can be justified by its formula. The formula for the speed is total distance travelled divided by the total time taken. i.e.,
$Speed = \dfrac{{total{\text{ }}distance{\text{ }}travelled}}{{total{\text{ }}time{\text{ }}taken}}$,
And we all know that the distance is a scalar quantity and distance cannot be negative. It can be zero but it cannot be negative, and also the time can never be zero or negative. So, the speed is the ratio of two quantities which are non-negative.
Hence the speed of a body cannot be negative in any condition.

Note:
One major difference between the distance and the displacement can be that the distance cannot be negative while the displacement can have both positive value and negative value as well as zero. This is because of the reason that the distance is a scalar quantity and displacement is a vector quantity. Displacement has both magnitude and direction and can have both values of positive and negative according to the direction of motion of the object from its reference point.