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Momentum and Impulse

Learn about momentum, impulse, elastic collisions, and more concepts in physics. Find out the key formulas and relationships to calculate momentum and impulse. Practice problems included.

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Momentum and Impulse

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  1. Momentum and Impulse Concepts of Physics Mr. Kuffer

  2. Momentum • Momentum can be defined as "mass in motion." All objects have mass; so if an object is moving, then it has momentum • Momentum depends upon the variables mass and velocity. • Momentum = mass * velocity • ρ = m * v • where m = mass and v=velocity

  3. We Know… • F = ma & a = v/t • So… F = m (v/t) OR… mv = Ft Impulse Momentum

  4. The Relationship & Units • Cause • Impulse (Impulse = Ft) • Measured in… N•s • Effect • Momentum, (ρ = mv) • Measured in … kg•m/s

  5. Momentum is a vector quantity • To fully describe the momentum of a 5-kg bowling ball moving westward at 2 m/s, you must include information about both the magnitude and the direction of the bowling ball • ρ = m * v • ρ = 5 kg * 2 m/s west • ρ = 10 kg * m / s west

  6. Elastic and inelastic Collisions • When a Ball hits the ground and sticks, the collision would be totally inelastic • When a Ball hits the ground and bounces to the same height, the collision is elastic • All other collisions are partially elastic collision

  7. A Reference Scale under-inflated basketball bouncing INELASTIC ELASTIC billiard balls colliding 100% 0% 90% 30% inflated basketball bouncing proton colliding with another proton Clay blob hitting ground

  8. Determine the momentum of a ... 60-kg halfback moving eastward at 9 m/s. ρ = mv = 60 kg ( 9 m/s ) 540 kg *m /s east 1000-kg car moving northward at 20 m/s. ρ = mv = 1000 kg ( 20 m/s ) 20,000 kg *m /s north Given: m = 60Kg v= 9 m/s Find : momentum (p) Given: m = 1000Kg v= 20 m/s Check Your Understanding

  9. Momentum and Impulse Connection • To stop such an object, it is necessary to apply a force against its motion for a given period of time • Impulse = F Δt = m Δv = Δρ Impulse = Change in momentum

  10. If the halfback experienced a force of 800 N for 0.9 seconds to the north, determine the impulse Impulse = F Δ t = m Δ v 800N ( 0.9s ) = 720 N*s the impulse was 720 N*s or a momentum change of 720 kg*m/s Given: F = 800 N t = 0.9 s Find : Impulse Check Your Understanding

  11. A 0.10 Kg model rocket’s engine is designed to deliver an impulse of 6.0 N*s. If the rocket engine burns for 0.75 s, what is the average force does the engine produce? Impulse = F Δ t = m Δ v 6.0 N*s = F ( 0.75s ) 6.0 N*s/ 0.75s = F 8.0 N = F Given: m = 0.10 Kg Impulse = 6 N* s t = 0.75s Find : Average Force Impulse Question #2

  12. A Bullet traveling at 500 m/s is brought to rest by an impulse of 50 N*s. What is the mass of the bullet? Impulse = F Δ t = m Δ v 50 N*s = m ( 500 m/s – 0 m/s ) 50 kg·m/s / 500 m/s = m 0.1 kg = m Given: v = 500 m/s Impulse = 50 N*s Find : m = ? Impulse Question # 3

  13. Summary • the impulse experienced by an object is the force*time • the momentum change of an object is the mass*velocity change • the impulse equals the momentum change

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