GATE CSE 2019 | GA | Question: 3

Question

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 _____.

• A. $1$
• B. $2$
• C. $3$
• D. $6$

Comments

bacha problem

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car 1--->50km/h

car 2--->60km/h

1hour ----->distance between them is 10km (car1---->50km in 1 hour and car 2------>60km in 1 hour )

2hour------->distance between them is 20km (120km-100km)

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Answer Here!   

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I also did this way only, common sense will work better than a formula

Answer 1

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

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

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

$T=2$

Answer 2

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

Answer 3

Elimination method :-

 

Given :-

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

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

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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.

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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.

 

Answer 4

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

Answer 5

In first hour car 1 will travel 50 car 2 will travel 60

In second hour car 1 will travel 100 and car 2 will travel 120 so d1 - d2 will 20 after two hours

Comments

B is correct

 

Answer 6

apply relative speed = 10km per hour

time = distance /speed

t= 20/10 =2 h