Question

What is the average speed of a Cheetah that sprints $100m$ in $\text{4}\,seconds$? What if it sprints $50m$ in $2\text{ }seconds$?
A. 25m/s, 25m/s
B. 20m/s, 30m/s
C. 45m/s, 40m/s
D. 55m/s, 60m/s

Answer 1

Hint: Average speed of an object is defined as the distance travelled by it in unit second. Distance travelled is the total path length covered by it.To calculate the average speed, calculate ratio of total distance travelled by the Cheetah and total time taken by Cheetah.

Complete answer:
Average speed of an object is given by total distance travelled by it in unit time. Mathematically, we can write this as
${{v}_{avg}}=\dfrac{d}{t}$
Where
${{v}_{avg}}=$ The average speed of the body
$d=$ Total distance travelled by the body
$t=$ Time taken
In this question, Cheetah travels 100 m in 4 seconds. Thus the average speed of the Cheetah is
$\begin{align}
  & {{v}_{avg}}=\dfrac{100}{4}m\text{ }{{\text{s}}^{-1}} \\
 & \text{ = 25 m }{{\text{s}}^{-1}} \\
\end{align}$
If Cheetah sprints 50 m in 2 seconds then its average speed is
$\begin{align}
  & {{v}_{avg}}=\dfrac{50}{2}m\text{ }{{\text{s}}^{-1}} \\
 & \text{ = 25 m }{{\text{s}}^{-1}} \\
\end{align}$

So, the correct answer is “Option A”.

Additional Information:
Displacement is defined as the minimum distance between the final and initial positions of the object. Displacement is a vector quantity. Therefore velocity is also a vector. Magnitude of a vector quantity can be either positive, zero or negative.
When the object moves in the same direction for a time period, the speed of the object is the same as its velocity during that time period.

Note:
Sometimes students get confused with terms velocity and speed. Velocity of a body is the displacement per unit time and is a vector quantity. Velocity of an object is denoted by $\vec{v}\text{ or }\mathbf{v}$(bold-faced). It depends on direction of motion.
Speed of the object is the distance travelled by it per unit time. Speed is a scalar and does not depend on direction of the motion.