Question

A man crosses a 500 m long street in 50 seconds. What is his speed in $m{\text{ }}{\sec ^{ - 1}}$?
A. 550 $m{\text{ }}{\sec ^{ - 1}}$
B. 450 $m{\text{ }}{\sec ^{ - 1}}$
C. 10 $m{\text{ }}{\sec ^{ - 1}}$
D. 25000 $m{\text{ }}{\sec ^{ - 1}}$

Answer 1

Hint: This type of questions can be solved using the distance-speed-time formula. In this formula if the two variables are known then the third variable can be found out.
According to the formula,
$\text{Distance} = \text{speed} \times \text{time}$
The speed can be found as required in the question.

Complete step-by-step solution:
Given,
$\text{Distance} = 500{\text{ }}m$
$\text{time} = {\text{50 sec}}$
$\text{speed} = ?$
Let the speed be S $m{\text{ }}{\sec ^{ - 1}}$,
Then from the formula,
$\text{distance} = \text{speed} \times \text{time}$
Putting the values of distance, speed and time
$ \Rightarrow 500 = S \times 50$
Dividing both sides by 50
$\dfrac{{500}}{{50}} = S$
Or,
$S = \dfrac{{500}}{{50}}$
On solving further,
$ \Rightarrow S = 10$
$\therefore $ The speed of the man is $10{\text{ m se}}{{\text{c}}^{ - 1}}$.
So option (c) is correct.

Note: As this type of question formula is being used therefore the formula is to be remembered. All the units should be changed into S.I. unit and then the question is to be solved otherwise the final answer would not come. Substitute the values of the variable in the equation carefully. Do not make any calculation mistake to avoid getting any wrong answer. If the final answer comes in decimal then do not forget to round it to its nearest decimal place if required. Always try to solve the question step by step. If the speed is required to be converted in kmph the use the equation $1{\text{ }}m{\text{ se}}{{\text{c}}^{ - 1}} = \dfrac{{18}}{5}km{\text{ h}}{{\text{r}}^{ - 1}}$ to convert mps to kph. For the quantity which is unknown, assume it is a variable and then solve for that variable after putting the known quantities in the equation.