Question

here is an intresting physics puzzle.
please don't scam for 5 points.​

Answer 1

Question:

A man rows to a place 48 km distant and come back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The speed of the stream is

Answer:

The speed of the stream is 1 km/hr

Explanation:

Let the speed of the stream be x km/hr and speed of the boat in still water be y km/hr

>> Speed of the boat upstream = (y - x) km/hr

>> Speed of the boat downstream = (y + x) km/hr

We know, Speed = distance/time

⇒ time = distance/speed

The man finds that he can row 4 km with the stream in the same time as 3 km against.

 $\implies \rm \dfrac{4 \: km}{(y+x) \: kmph}=\dfrac{3 \: km}{(y-x) \: kmph} \\\\ \implies \rm 4(y-x)=3(y+x) \\\\ \implies \rm 4y-4x=3y+3x \\\\ \implies \rm 4y-3y=3x+4x \\\\ \implies \boxed{\bf y=7x}$

The man rows to a place 48 km distant and come back in 14 hours.

time taken to cover 48 km upstream = 48/(y - x) hr

time taken to cover 48 km downstream = 48/(y + x) hr

 

Hence,

 $\implies \sf \dfrac{48}{y-x}+\dfrac{48}{y+x}=14 \\\\ \implies \sf 48 \bigg(\dfrac{1}{y-x}+\dfrac{1}{y+x} \bigg)=14 \\\\ \implies \sf \dfrac{1}{y-x}+\dfrac{1}{y+x}=\dfrac{14}{48} \\\\ \implies \sf \dfrac{1}{7x-x}+\dfrac{1}{7x+x}=\dfrac{7}{24} \\\\ \implies \sf \dfrac{1}{6x}+\dfrac{1}{8x}=\dfrac{7}{24} \\\\ \implies \sf \dfrac{1}{x} \bigg(\dfrac{8+6}{8 \times 6} \bigg)=\dfrac{7}{24} \\\\ \implies \sf \dfrac{1}{x} \times \dfrac{14}{48}=\dfrac{7}{24}$

 $\implies \sf \dfrac{1}{x}=\dfrac{7}{24} \times \dfrac{48}{14} \\\\ \implies \sf \dfrac{1}{x}=1 \\\\ \implies \boxed{\bf x=1 \ km/hr}$

Therefore, the speed of the stream is 1 kmph

Answer 2

Answer:

no bhai nhi chahiye twinkle wala joke acha h