Question

A person crosses 600 m in 5 minutes. Find speed in km/hr.

• A. 3.6
• B. 7.2
• C. 8.4
• D. 10

Hint:

Memorize the conversion factors: $1 \text{ km/hr} = \frac{5}{18} \text{ m/s}$ and $1 \text{ m/s} = \frac{18}{5} \text{ km/hr}$. This makes conversions between these common speed units very fast.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The problem asks to calculate speed in kilometers per hour, given distance in meters and time in minutes. This requires unit conversions.

Step 2: Key Formula or Approach:
1. Speed = $\frac{\text{Distance}}{\text{Time}}$.
2. Convert meters to kilometers (1 km = 1000 m).
3. Convert minutes to hours (1 hour = 60 minutes).
4. Alternatively, use the conversion factor: $1 \text{ m/s} = \frac{18}{5} \text{ km/hr}$.

Step 3: Detailed Explanation:
Given:
- Distance ($D$) = 600 m.
- Time ($T$) = 5 minutes.
Method 1: Step-by-step conversion
1. Convert distance to km:
$D = 600 \text{ m} = \frac{600}{1000} \text{ km} = 0.6 \text{ km}$.
2. Convert time to hours:
$T = 5 \text{ minutes} = \frac{5}{60} \text{ hours} = \frac{1}{12} \text{ hours}$.
3. Calculate speed in km/hr:
Speed = $\frac{D}{T} = \frac{0.6 \text{ km}}{1/12 \text{ hr}} = 0.6 \times 12 \text{ km/hr} = 7.2 \text{ km/hr}$.
Method 2: Convert to m/s first, then to km/hr
1. Calculate speed in m/s:
$T = 5 \text{ minutes} = 5 \times 60 = 300 \text{ s}$.
Speed = $\frac{600 \text{ m}}{300 \text{ s}} = 2 \text{ m/s}$.
2. Convert speed from m/s to km/hr:
Speed = $2 \text{ m/s} \times \frac{18}{5} \text{ km/hr per m/s}$
Speed = $\frac{36}{5} \text{ km/hr} = 7.2 \text{ km/hr}$.

Step 4: Final Answer:
The speed in km/hr is 7.2.