objective: mcas review- momentum homework: finish questions

ObjectiveObjective: : MCAS MCAS review- Momentumreview- Momentum

Homework: Finish Homework: Finish questionsquestions

Vectors vs. ScalarsVectors vs. Scalars

Vectors: Vectors: size (magnitude) and size (magnitude) and directiondirection

Example- 20m/s North (velocity)Example- 20m/s North (velocity)

Scalars:Scalars: Just size (magnitude) Just size (magnitude)

Example- 20m/s (speed)Example- 20m/s (speed)

Do Now:Do Now:

Answer questions on Vectors Answer questions on Vectors vs Scalarsvs Scalars

Vectors vs. ScalarsVectors vs. Scalars

Common vectors:Common vectors: anything with magnitude anything with magnitude (size) (size) and directionand direction

Velocity, Force, Acceleration, Velocity, Force, Acceleration, displacementdisplacement

Common Scalars:Common Scalars: anything just magnitude anything just magnitude (size)(size)

Mass, temperature, distance, energyMass, temperature, distance, energy

Which of the following is an Which of the following is an example of a vector quantity? example of a vector quantity?

A.A student walks 2.0 km north. A.A student walks 2.0 km north. B.An object has a mass of 10.5 B.An object has a mass of 10.5 kg. kg.

C.A 1.0 kg object moves at 18 m/s.C.A 1.0 kg object moves at 18 m/s. D.A ball has an instantaneous D.A ball has an instantaneous speed of 15 m/s. speed of 15 m/s.

Which of the following is a scalarWhich of the following is a scalarquantity?quantity?

A.the mass of a brick A.the mass of a brick B.the velocity of a falling tennis B.the velocity of a falling tennis ball ball

C.the force required to lift aC.the force required to lift a10 kg mass 10 kg mass

D.the acceleration of a toy car D.the acceleration of a toy car overovera 60 s perioda 60 s period

Which of the following is a Which of the following is a vectorvectorquantity?quantity?

A.mass A.mass B.force B.force C.temperature C.temperature D.kinetic energyD.kinetic energy

To calculate the momentum of a pickupTo calculate the momentum of a pickuptruck with a velocity of 25 m/s east, truck with a velocity of 25 m/s east, ititis also necessary to know which of theis also necessary to know which of thefollowing?following?

A.time elapsedA.time elapsed B.drive force of the motor B.drive force of the motor C.mass of the pickup truck C.mass of the pickup truck D.distance that the pickup travelsD.distance that the pickup travels

Use steps to solveUse steps to solve

How to cheat using the How to cheat using the formula sheetformula sheet

1.1. Find what the question is Find what the question is asking for (underline)asking for (underline)

2.2. Look up what’s underlined Look up what’s underlined and find variable for itand find variable for it

3.3. Find equation that is for Find equation that is for that variablethat variable

4.4. Read equation like Read equation like sentence (may need to look sentence (may need to look up what other variables up what other variables man in the equation)man in the equation)

5.5. Answer or solve the Answer or solve the problemproblem

(if problem, use 4 steps for (if problem, use 4 steps for problem solving)problem solving)

Ex: “What is Ex: “What is work?”work?”

Ex: W = WorkEx: W = Work

Ex: W = FdEx: W = Fd

Ex:Ex: Work is Work is force force multiplied multiplied by distanceby distance

To calculate the momentum of a pickupTo calculate the momentum of a pickuptruck with a velocity of 25 m/s east, truck with a velocity of 25 m/s east, ititis also necessary to know which of theis also necessary to know which of thefollowing?following?

A.time elapsedA.time elapsed B.drive force of the motor B.drive force of the motor C.mass of the pickup truck C.mass of the pickup truck D.distance that the pickup travelsD.distance that the pickup travels


Reminder: velocity is same as speed, but with direction

Use formula sheet to find what Momentum is:

p =mv

We now remember We now remember that momentum is that momentum is mass x velocity, mass x velocity, so…so…

A 600 g basketball, a 57 g tennis A 600 g basketball, a 57 g tennis ball, a 46 g golf ball, and a 2.7 ball, a 46 g golf ball, and a 2.7 g table tennis ball are moving g table tennis ball are moving with the same velocity. Which ball with the same velocity. Which ball has the has the greatestgreatest momentum? momentum?

A.golf ballA.golf ball B.basketball B.basketball C.tennis ball C.tennis ball D.table tennis ballD.table tennis ball

If all have same velocity, then one with the biggest mass would give the biggest momentum (multiplying by the biggest number)


p =mv


What is the momentum of a metal What is the momentum of a metal discdiscwith a mass of 1.5 kg sliding on with a mass of 1.5 kg sliding on aafrictionless surface at 0.75 m/s?frictionless surface at 0.75 m/s?

A.0.50 kg • m/s A.0.50 kg • m/s B.0.85 kg • m/s B.0.85 kg • m/s C.1.1 kg • m/s C.1.1 kg • m/s D.2.0 kg • m/sD.2.0 kg • m/s

4 steps for problem 4 steps for problem solving solving (calculations)(calculations)•• – – 1.1. Write the equation (for what Write the equation (for what

underlined)underlined)

– – 2.2. Replace the Replace the knownknown values values

(everything with units and numbers- (everything with units and numbers- circle these when read problem)circle these when read problem)

(Not all values are what you want- check (Not all values are what you want- check with the equation from step 1)with the equation from step 1)

– – 3.3. Solve the problemSolve the problem

-- 4. Label with the correct unit -- 4. Label with the correct unit of measurement.of measurement.





p =mv

What happens to the cart’s What happens to the cart’s speed when the block lands speed when the block lands in it?in it?

3. The diagrams below show a cart 3. The diagrams below show a cart moving with a velocity, V, on a moving with a velocity, V, on a frictionless surface as a wooden block frictionless surface as a wooden block is being dropped. The block then falls is being dropped. The block then falls straight down onto the moving cart.straight down onto the moving cart.

Which of the following statements Which of the following statements describes what will happen after thedescribes what will happen after theblock lands on the moving cart?block lands on the moving cart?

A.The cart will move to the left atA.The cart will move to the left ata velocity less than the originala velocity less than the originalvelocity of the cart. velocity of the cart.

B.The cart will move to the left atB.The cart will move to the left ata velocity greater than the originala velocity greater than the originalvelocity of the cart. velocity of the cart.

C.The cart will move to the right atC.The cart will move to the right ata velocity less than the originala velocity less than the originalvelocity of the cart. velocity of the cart.

D.The cart will move to the right atD.The cart will move to the right ata velocity greater than the originala velocity greater than the originalvelocity of the cart.velocity of the cart.

Must remember that momentum is conserved!

What you start with is what you end with.

mV = M___

v

mv before = mv after

If mass increases, then speed must decrease in order for momentum to be conserved!

Can use conservation of Can use conservation of momentum law to solve momentum law to solve momentum collision momentum collision problemsproblems

p p beforebefore = = p p afterafter

mv mv beforebefore = mv = mv afterafter

A 1 kg block sliding to the right on a A 1 kg block sliding to the right on a level, frictionless surface with a level, frictionless surface with a speed of 2 m/s collides and sticks to speed of 2 m/s collides and sticks to a second 1 kg block sliding to the a second 1 kg block sliding to the left. left.

After the collision, the blocks are After the collision, the blocks are motionless. What was the speed of the motionless. What was the speed of the second 1 kg block before the second 1 kg block before the collision? collision?

A.1 m/s B.2 m/s C.3 m/s D.4 m/sA.1 m/s B.2 m/s C.3 m/s D.4 m/s

It’s a collision, and they give us the velocity and mass, so we know it going to be a conservation of momentum problem

p before = p after

mv1 + mv2 = 0

1x2 + 1x v = 02 + v = 0

v = -2

Write in notesWrite in notes

What two things determine What two things determine momentum?momentum?

objective: mcas review- momentum homework: finish questions

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