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8 votes
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Two cars at the same time from the same location and go in the same direction. The speed of the first car is $50$ km/h and the speed of the second car is $60$ km/h. The number of hours it takes for the distance between the two cars to be $20$ km is _____.

  1. $1$
  2. $2$
  3. $3$
  4. $6$
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4 Answers

Best answer
19 votes
19 votes
Let the required distance be reached at time $T$. Let Speed be ($S1=60 ,S2=50$)

According to the Question $\rightarrow D1- D2=20$

$\therefore (60*T)-(50*T)=20$

$T=2$
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7 votes
7 votes
Given Distance =20km/hr

First find the Relative speed

Relative speed=60km/h-5 km/h=10km/h

Speed=Distance/time

Time=20/10= 2hrs
5 votes
5 votes

Elimination method :-

 

Given :-

car $1$ speed = $50\ km/h$

car $2$ speed = $60\ km/h$


car $1$ travels $50$ km in $1$ hr

car $2$ travels $60$ km in $1$ hr

So distance between them is $10$ km in $1$ hr.

so option A eliminated.


car $1$ travels $100$ km in $2$ hr

car $2$ travels $120$ km in $2$ hr

so distance between them is $20$ km in $2$ hr.

$\therefore$ option B is correct answer.

 

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3 votes
3 votes
Relative speed 10km/hr so separation increases at the rate of 10 per hour so requires 2 hours
Answer:

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