To find the speed of the stream, we can use the information given about the motorboat's journey upstream and downstream. Let's break it down step by step.
Given Information
- Speed of the motorboat in still water: 18 km/hr
- Distance traveled: 24 km
- Time difference: 1 hour more upstream than downstream
Speed Calculations
Let the speed of the stream be x km/hr.
The effective speed of the boat upstream is (18 - x) km/hr, and downstream it is (18 + x) km/hr.
Time Formulas
The time taken to travel upstream is:
Time upstream = Distance / Speed = 24 / (18 - x)
The time taken to travel downstream is:
Time downstream = Distance / Speed = 24 / (18 + x)
Setting Up the Equation
According to the problem, the time taken upstream is 1 hour more than the time taken downstream:
24 / (18 - x) = 24 / (18 + x) + 1
Solving the Equation
To solve for x, we can cross-multiply and simplify:
- 24(18 + x) = 24(18 - x) + (18 - x)(18 + x)
- 24(18 + x) - 24(18 - x) = (18 - x)(18 + x)
- 48x = 324 - x²
- x² + 48x - 324 = 0
Finding the Roots
Using the quadratic formula x = [-b ± √(b² - 4ac)] / 2a, where a = 1, b = 48, and c = -324:
x = [-48 ± √(48² + 4 × 324)] / 2
Calculating this gives us two potential solutions for x.
Final Result
After solving, we find that the speed of the stream is 6 km/hr.
Answer
The speed of the stream is A. 6 km/hr.