A truck crosses a man moving along the road at 6 km/hr. The man could see the truck upto 2 min find the speed of the truck, if at the time of disappearance the distance of truck to man is 1.2 km

Options

A. 4.2 km/hr
B. 42 km/hr
C. 35 km/hr
D. 45 km/hr

Answer

To solve the problem step by step, we will follow these calculations:

### Step 1: Understand the problem
A truck crosses a man who is moving at a speed of 6 km/hr. The man can see the truck for 2 minutes before it disappears. At the moment the truck disappears from view, it is 1.2 km away from the man.

### Step 2: Convert time from minutes to hours
Since the speed is given in km/hr, we need to convert the time from minutes to hours.
- 2 minutes = 2/60 hours = 1/30 hours.

### Step 3: Use the formula for relative speed
The relative speed of the truck with respect to the man is the difference between the speed of the truck (let's denote it as x km/hr) and the speed of the man (6 km/hr). Therefore, the relative speed is:
- Relative Speed = x - 6 km/hr.

### Step 4: Set up the equation using distance
The truck travels a distance of 1.2 km in the time of 2 minutes (or 1/30 hours). Using the formula for speed:
- Speed = Distance / Time,
we can rearrange this to find the relative speed:
- Relative Speed = Distance / Time = 1.2 km / (1/30 hr) = 1.2 km * 30 = 36 km/hr.

### Step 5: Create the equation
Now we can set up the equation based on the relative speed:
- x - 6 = 36.

### Step 6: Solve for x
To find the speed of the truck (x), we solve the equation:
- x - 6 = 36
- x = 36 + 6
- x = 42 km/hr.

### Step 7: Conclusion
The speed of the truck is 42 km/hr.