UGC NET CSE | October 2020 | Part 1 | Question: 24

Question

In a $100$ meters race, $A$ beat $B$ by $10$ meter or $2$ second. What is the speed of $A$?

• A. $5$ Km/h
• B. $10$ Km/h
• C. $15$ Km/h
• D. $20$ Km/h

Answer 1

We know both of them covers 100 m, but

t(B) = t(A) +2

For last 10m, B took 2 sec more to cover that distance, hence

Speed of B = 5 m/sec

B covered 100 meters in 20 sec so,

A covered 100 meters in 18 sec

Speed of A = 100/18 * 18/5 = 20 Km/h

Answer 2

D. 20 Km/h ..

 

Distance to cover = 100 m ...

 

## Formula used:

Distance = Speed × Time ..

 

 Concept used:

To convert m/s to km/h then multiply with 18/5 ..

 

 Calculation:

A beats B by 10 meters or 2 seconds means B covers 10 meters distance in 2 seconds ..

 

 Speed of B

= 10/2

= 5 m/s ..

 

Total time is taken by B to complete 100 m race

= 100/5

= 20 seconds ..

 

A takes 2 seconds less to complete the race ..

Time is taken by A to complete the race

= 20 – 2

= 18 sec

 

Speed of A =

100/18 m/s

= (100/18) × (18/5)

= 20 km/h ..

 

The speed of A is 20 km/h ..