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Question

Answers

A. \[\dfrac{1}{30}\]

B. \[\dfrac{2}{5}\]

C. 2

D. 30

Answer
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Given two planes at speed of 600miles per hour and at 720 miles per hour

And we are asked to find extra distance in miles by the faster airplane in 12 seconds than the slower airplane

So first we will convert speed in terms of seconds by using formula

\[1hour=60\times 60\sec onds\]

\[600\dfrac{miles}{hour}=600\dfrac{miles}{60\times 60\sec ond}=0.167\dfrac{miles}{\sec ond}\]

Similarly \[720\dfrac{miles}{hour}=720\dfrac{miles}{60\times 60\sec ond}=0.2\dfrac{miles}{\sec ond}\]

Now the distance travelled by both planes in 12 seconds is

\[0.167\dfrac{miles}{\sec ond}\times 12\sec onds=2.004miles\]

\[0.2\dfrac{miles}{\sec ond}\times 12\sec ond=2.4miles\]

To find how many more miles can the faster airplane travel in 12 seconds than the slower airplane, this line basically means that we have to find extra distance travelled by faster plane than slower one

It means we just have to subtract both the distances

Distance by faster plane – Distance by the slower plane

\[2.4miles-2.004miles\simeq 0.4miles\]

\[0.4miles=\dfrac{2}{5}miles\]

Relative speed \[v=720-600=120\dfrac{miles}{hour}\]

Now multiple v with 12 seconds \[s=12\times 120=1440\dfrac{miles}{hour}\sec onds\]

\[s=1440\dfrac{miles}{3600}=0.4=\dfrac{2}{5}\]