Dashi Science Lecture: Newton's Third Law of Motion

Introduction

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• Current Topic: Newton's Third Law of Motion.

Key Concept: Newton's Third Law

• Statement: For every action, there is an equal and opposite reaction.
• Formula: ( p = mv )
  • ( p ): Momentum (kg·m/s)
  • ( m ): Mass (kg)
  • ( v ): Velocity (m/s)

Solving the Formula

• Triangle Method: Helps determine whether to multiply or divide.
  • Solving for ( p ): Cover ( p ), calculate ( m imes v ).
  • Solving for ( m ): Cover ( m ), calculate ( \frac{p}{v} ).
  • Solving for ( v ): Cover ( v ), calculate ( \frac{p}{m} ).

Practice Problems

Example 1: Calculating Momentum

• Problem: A 4000 kg truck travels at 10 m/s. What is the momentum?
• Solution:
  1. Use formula: ( p = mv )
  2. ( m = 4000 ) kg, ( v = 10 ) m/s
  3. Calculate: ( 4000 imes 10 = 40000 ) kg·m/s

Example 2: Calculating Mass

• Problem: A beach ball rolls at 0.5 m/s with a momentum of 0.25 kg·m/s. What is the mass?
• Solution:
  1. Use formula: ( m = \frac{p}{v} )
  2. ( p = 0.25 ) kg·m/s, ( v = 0.5 ) m/s
  3. Calculate: ( \frac{0.25}{0.5} = 0.5 ) kg

Example 3: Calculating Velocity

• Problem: An 8 kg bowling ball rolls with a momentum of 16 kg·m/s. How fast is it traveling?
• Solution:
  1. Use formula: ( v = \frac{p}{m} )
  2. ( p = 16 ) kg·m/s, ( m = 8 ) kg
  3. Calculate: ( \frac{16}{8} = 2 ) m/s

Conclusion

• Concept Mastery: Now you know how to solve ( p = mv ).
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