Question

Find the distance covered by a car moving at 20 m/s for 3h.
A) 220 km
B) 218 km
C) 216 km
D) 230 km

Answer 1

Hint: Here first assume the distance covered by the car to be x
Then we will use the formula for speed and evaluate the value of distance x.
The speed is given by:-
$$\text{speed}={\displaystyle \frac{\text{distance}}{\text{time}}}$$

Complete step-by-step answer:
Let the distance covered by the car be x
Now we are given that:-
Speed of the car is 20 m/s
The time taken by the car is 3 hours.
Since the time is given in hours and speed is given in m/s so we need to make the unit of time the same.
Hence in order to make the unit same, we will convert hours into seconds
Now since we know that:-
$$1hr=60min$$ and $$1min=60\sec$$
Therefore,
$$1hr=60\times 60\sec$$
Hence 3hr will be equal to:-
$$3hr=3\times 60\times 60\sec$$
Calculating the value we get:-
$$3hr=10800\sec$$
Now we know that the speed is given by:-
$$\text{speed}={\displaystyle \frac{\text{distance}}{\text{time}}}$$
Hence putting in the respective values we get:-
$$20={\displaystyle \frac{x}{10800}}$$
Now evaluating for the value of x we get:-
$$\begin{gathered} x=20\times 10800 \\ \Rightarrow x=216000m \end{gathered}$$
Therefore, the distance covered is 216000 m
Now we will convert this distance into kilometers.
We know that:
$$\begin{gathered} 1km=1000m \\ \Rightarrow 1m={\displaystyle \frac{1}{1000}}km \end{gathered}$$
Hence 216000m will be equal to:-
$$216000m={\displaystyle \frac{216000}{1000}}km$$
Calculating the value we get:-
$$216000m=216km$$
Hence the distance covered by the car is 216 km

So, the correct answer is “Option C”.

Note: Students can also convert the speed from m/s to km/hour and then put the respective values in the formula for speed to get the value of distance covered.
$$1m/\sec ={\displaystyle \frac{18}{5}}km/hr$$