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## PowerPoint Slideshow about ' Physics' - shaeleigh-harper

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Momentum and its Conservation

- Let’s check our knowledge (1-12)

What two things must an object have to have momentum?

- Mass (kg)
- Velocity (m/s)

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?

- Multiple mass by velocity
- Momentum = mv

What is the symbol and unit for momentum?

- p (actually rho-)
- kgm/s

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?

- Force
- Time interval

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?

- Multiply force applied by time of application
- Impulse = Ft

What is the unit for impulse?

- N•s
- There is no symbol for impulse!

Are momentum and impulse vector quantities?

- Yes
- They both have magnitude (size) and direction

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 = mv/t
- Ft = mv (fat mav)

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

- Ft = p2 – p1
- FΔt = mΔv
- Impulse (Ft) 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:

- 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 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.

- 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 (Ft = mv)

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

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

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 applies the brakes for 2 s and the brakes apply an average force of 5000N. Find:

- For every action there is an equal and opposite reaction

State the Law of Conservation of Momentum applies the brakes for 2 s and the brakes apply an average force of 5000N. Find:

- 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? applies the brakes for 2 s and the brakes apply an average force of 5000N. Find:

- A system where mass is not lost or gained.

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? forces on a system?

- When no external forces act upon the system.

How is an isolated system different from a closed system? forces on a system?

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

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

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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