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Physics. Chapter 9 Momentum and its Conservation. Momentum and its Conservation. Let’s check our knowledge (1-12). Define momentum. Momentum The quantity of motion The property of an object in motion. What two things must an object have to have momentum?. Mass (kg) Velocity (m/s).

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Physics

Physics

Chapter 9

Momentum and its Conservation


Momentum and its conservation

Momentum and its Conservation

  • Let’s check our knowledge (1-12)


Define momentum

Define momentum.

Momentum

  • The quantity of motion

  • The property of an object in motion


What two things must an object have to have momentum

What two things must an object have to have momentum?

  • Mass (kg)

  • Velocity (m/s)


Explain how inertia is different than momentum

Explain how inertia is different than momentum.

  • Inertia is a property of any object with mass

  • It is the tendency of an object to resist a change in its velocity

  • Momentum is a property of an object in motion

  • A stationary object has no (O) momentum

  • An object must be moving to have momentum but not inertia


How do you calculate momentum

How do you calculate momentum?

  • Multiple mass by velocity

  • Momentum = mv


What is the symbol and unit for momentum

What is the symbol and unit for momentum?

  • p (actually rho-)

  • kgm/s


Define impulse

Define impulse.

  • Force applied to an object over a time interval to change its momentum


What two things must an object have to have impulse

What two things must an object have to have impulse?

  • Force

  • Time interval


Explain how impulse is different than momentum

Explain how impulse is different than momentum.

  • Momentum is the property of an object in motion.

  • Impulse is force applied for a certain time that causes an object’s momentum to change.


How do you calculate impulse

How do you calculate impulse?

  • Multiply force applied by time of application

  • Impulse = Ft


What is the unit for impulse

What is the unit for impulse?

  • N•s

  • There is no symbol for impulse!


Are momentum and impulse vector quantities

Are momentum and impulse vector quantities?

  • Yes

  • They both have magnitude (size) and direction


Physics

Use Newton’s Second law of Motion and the definition of acceleration to derive the relationship between impulse and change in momentum.

  • F = ma and a = v/t

  • F = mv/t

  • Ft = mv (fat mav)


Write down the impulse momentum theorem explain it in words

Write down the Impulse- Momentum Theorem. Explain it in words.

  • Ft = p2 – p1

  • FΔt = mΔv

  • Impulse (Ft) on an object causes its initial momentum (p1) to change to its final momentum (p2).


If a tennis ball is hit by a racket for 0 15 s with a force of 23 n find its

If a tennis ball is hit by a racket for 0.15 s with a force of 23 N find its:

  • Beginning momentum

  • Impulse given it by the racket

  • Change in momentum

  • Final momentum


If a tennis ball is hit by a racket for 0 15 s with a force of 23 n find its1

If a tennis ball is hit by a racket for 0.15 s with a force of 23 N find its:

  • Beginning momentum: 0 kg*m/s

  • Impulse given it by the racket: 3.45 N*s

  • Change in momentum: 3.45 kg*m/s

  • Final momentum: 3.45 kg*m/s


Explain using the terms momentum and impulse why automobile airbags save lives

Explain using the terms momentum and impulse why automobile airbags save lives.

  • When a person stops there is the same change in momentum with or without the airbag.

  • The airbag increases the time for the force so it is less (Ft = mv)


A 725 kg compact car is moving at 100 km h towards the east find its momentum kg m s

A 725 kg compact car is moving at 100 km/h towards the east. Find its momentum (kg*m/s)

  • 100 km/h = 27.8 m/s (?)

  • p = mv = (725)(27.8) = 20155 kg*m/s


Physics

If the driver of the 725 kg car traveling at 27.8 m/s, applies the brakes for 2 s and the brakes apply an average force of 5000N. Find:

  • The impulse given to the car

  • The car’s change in momentum

  • The car’s final momentum

  • The car’s final velocity


Physics

If the driver of the 725 kg car traveling at 27.8 m/s, applies the brakes for 2 s and the brakes apply an average force of 5000N. Find:

  • The impulse given to the car: - 10,000 N*s

  • The car’s change in momentum: - 10,000 kg*m/s

  • The car’s final momentum: 10,155 kg*m/s

  • The car’s final velocity: 14 m/s


State newton s third law of motion

State Newton’s Third Law of Motion

  • For every action there is an equal and opposite reaction


State the law of conservation of momentum

State the Law of Conservation of Momentum

  • The momentum of any closed, isolated system doesn't change

  • In a closed, isolated system, the initial momentum is equal to the final momentum


What is a closed system

What is a closed system?

  • A system where mass is not lost or gained.


What is the difference between internal forces and external forces on a system

What is the difference between internal forces and external forces on a system?

  • Internal forces are those forces that act within the system.

  • External force are forces acting on the system from the outside (the surroundings)


What is an isolated system

What is an isolated system?

  • When no external forces act upon the system.


How is an isolated system different from a closed system

How is an isolated system different from a closed system?

  • A closed system can have an outside force acting upon it but an isolated system cannot.


Physics

For the Law of Conservation of Momentum to be true, must a system be closed or isolated or both. Explain.

  • An isolated system is also closed, so it must be isolated (and thus also closed).

  • If only closed momentum can still be transferred to it by way of an outside force


Physics

If there is no air in outer space for a rocket to push off of, explain how when a rocket fires its engines in space it can move.

  • The escaping gas pushes off the rocket and the rocket pushes off the gas with the same force.

  • This causes and equal and opposite change in momentum for both

  • So both move but in opposite directions (and speeds)


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