A wide hose pipe is held horizontally by fireman.It delivers water through a nozale at one lirte per second. On increasing the pressure, this increass to two litres per second.The fireman has now to

Options

A. push forward twice as hard
B. pulsh forward four times as hard
C. push backward four times as hard
D. push backward twice as hard

Answer

To solve the problem, we need to analyze the situation involving the flow of water through a hose pipe and how the force exerted by the fireman changes when the flow rate of water increases.

### Step-by-Step Solution:

1. **Understanding the Initial Flow Rate**:
- The hose pipe initially delivers water at a rate of 1 liter per second. This can be denoted as \( Q_1 = 1 \, \text{L/s} \).

2. **Understanding the Increased Flow Rate**:
- After increasing the pressure, the flow rate increases to 2 liters per second. This can be denoted as \( Q_2 = 2 \, \text{L/s} \).

3. **Relating Flow Rate to Force**:
- The force exerted by the fireman can be related to the flow rate of water. The force \( F \) required to maintain the flow can be expressed as:
\[ F \propto Q^2 \]
- This means that the force is proportional to the square of the flow rate.

4. **Calculating the Ratio of Forces**:
- Using the relationship \( F_1/F_2 = Q_1^2/Q_2^2 \):
\[ F_1/F_2 = (1^2)/(2^2) = 1/4 \]
- Therefore, \( F_2 = 4 \times F_1 \).

5. **Conclusion**:
- Since the force exerted by the fireman must increase to maintain the increased flow rate, the fireman must push forward 4 times as hard to counteract the increased reaction force from the water flow.

### Final Answer:
The fireman has to push forward **four times as hard**.