A motor car needs an engine of 7500 watt to keep it moving with a constant velocity of 20 m/s on horizontal road. The force of fric­tion between the car tyres and the ground is

Options

A. 375 dyne
B. 375 newton
C. `1.5 xx 10^(5)` newton
D. `1.5 xx 10^(5)` dyne

Explanation

To find the force of friction between the car tires and the ground, we can use the relationship between power, force, and velocity. The power (P) required to keep the car moving at a constant velocity is given by the formula:

\[ P = F \cdot v \]

Where:
- \( P \) is the power in watts (7500 W),
- \( F \) is the force of friction in newtons (N),
- \( v \) is the velocity in meters per second (20 m/s).

### Step-by-Step Solution:

1. **Identify the given values:**
- Power \( P = 7500 \) watts
- Velocity \( v = 20 \) m/s

2. **Write the formula for power:**
\[ P = F \cdot v \]

3. **Rearrange the formula to solve for force \( F \):**
\[ F = \frac{P}{v} \]

4. **Substitute the known values into the equation:**
\[ F = \frac{7500 \, \text{W}}{20 \, \text{m/s}} \]

5. **Calculate the force:**
\[ F = \frac{7500}{20} = 375 \, \text{N} \]

6. **Conclusion:**
The force of friction between the car tires and the ground is \( 375 \, \text{N} \).

### Final Answer:
The force of friction between the car tires and the ground is **375 N**.

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