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To solve this problem, we can use the following formulas from physics:

1. **Calculate the impact velocity using gravitational potential energy**:  
   When the ball falls from a height \( h \) and reaches the ground, its potential energy is converted to kinetic energy. We use:
   \[
   v_{\text{impact}} = \sqrt{2gh}
   \]
   where:
   - \( g \) is the acceleration due to gravity (\( 9.8 \, \text{m/s}^2 \)),
   - \( h = 10 \, \text{m} \) is the height.

2. **Calculate the rebound velocity**:  
   Since the ball rebounds with 99% of its incident speed, we find the rebound velocity \( v_{\text{rebound}} \) by:
   \[
   v_{\text{rebound}} = 0.99 \times v_{\text{impact}}
   \]

3. **Impulse-Momentum Theorem**:  
   The average net force \( F_{\text{avg}} \) during the collision can be related to the change in momentum over the contact time \( \Delta t \) by:
   \[
   F_{\text{avg}} = \frac{\Delta p}{\Delta t}
   \]
   where \( \Delta p \) is the change in momentum, calculated by:
   \[
   \Delta p = m \left( v_{\text{rebound}} - (-v_{\text{impact}}) \right) = m \left( v_{\text{rebound}} + v_{\text{impact}} \right)
   \]
   Here, \( m = 0.025 \, \text{kg} \) (since 25 grams = 0.025 kg).

4. **Solve for the time \( \Delta t \)**:  
   Rearranging the impulse-momentum equation to solve for \( \Delta t \):
   \[
   \Delta t = \frac{\Delta p}{F_{\text{avg}}}
   \]

With these formulas, we can calculate each step to find the time the ball was in contact with the ground.

Would you like to see the full calculations step-by-step? 

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### Related Questions
1. What would happen to the contact time if the rebound velocity was only 80% of the impact velocity?
2. How does the force change if the ball mass is doubled but other conditions remain the same?
3. What if the ball falls from a different height, say 15 meters; how does that affect the contact time?
4. How would this problem change if the ball didn't rebound at all after hitting the ground?
5. How does the impulse-momentum theorem apply in real-world applications like airbags?

### Tip
The impulse-momentum theorem is very useful in situations involving collisions or sudden changes in velocity, helping to relate force, time, and change in momentum.

Starting from rest, a 25 g bouncy ball falls from a height of 10 m onto a flat, horizontal surface and rebounds with 99% of its incident speed. Find the amount of time that the ball was in contact with the ground if the average net force on the ball during the collision is 45 N.

Learn how to calculate the time a 25g bouncy ball is in contact with the ground after falling from 10m and rebounding with 99% of its impact speed. This problem covers kinematics, impulse-momentum theorem, and energy conservation, and is suitable for students in Grades 11-12.

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