A girl weighing 25 kg stands on the floor. She exerts a downward force of 250 N on the floor. What force does the floor exert on her ?

Answer

To solve the problem, we need to understand the forces acting on the girl and apply Newton's third law of motion. Here’s a step-by-step solution:

### Step 1: Identify the weight of the girl
The weight of an object is calculated using the formula:
\[ \text{Weight} = \text{mass} \times \text{acceleration due to gravity} \]
Given that the mass of the girl is 25 kg and the acceleration due to gravity is approximately \( 9.8 \, \text{m/s}^2 \):
\[ \text{Weight} = 25 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 245 \, \text{N} \]

### Step 2: Understand the forces acting on the girl
The girl is standing on the floor and exerts a downward force of 250 N on the floor. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. This means that if the girl exerts a force of 250 N downward, the floor will exert an equal force of 250 N upward on her.

### Step 3: Conclusion
Since the girl exerts a downward force of 250 N on the floor, the floor exerts an upward force of 250 N on her. Therefore, the force that the floor exerts on her is:
\[ \text{Force exerted by the floor} = 250 \, \text{N} \]

### Final Answer
The force that the floor exerts on her is **250 N**.

---