Objective: MCAS review- Momentum Homework: Finish questions

Vectors vs. Scalars Vectors: size (magnitude) and direction Example- 20m/s North (velocity) Scalars: Just size (magnitude) Example- 20m/s (speed)

Do Now: Answer questions on Vectors vs Scalars

Vectors vs. Scalars Common vectors: anything with magnitude (size) and direction Velocity, Force, Acceleration, displacement Common Scalars: anything just magnitude (size) Mass, temperature, distance, energy

Which of the following is an example of a vector quantity?  A.A student walks 2.0 km north.  B.An object has a mass of 10.5 kg.  C.A 1.0 kg object moves at 18 m/s.  D.A ball has an instantaneous speed of 15 m/s. 

Which of the following is a scalar quantity?  A.the mass of a brick  B.the velocity of a falling tennis ball  C.the force required to lift a 10 kg mass  D.the acceleration of a toy car over a 60 s period

Which of the following is a vector quantity?  A.mass  B.force  C.temperature  D.kinetic energy

Use steps to solve To calculate the momentum of a pickup truck with a velocity of 25 m/s east, it is also necessary to know which of the following?  A.time elapsed  B.drive force of the motor  C.mass of the pickup truck  D.distance that the pickup travels

How to cheat using the formula sheet Find what the question is asking for (underline) Look up what’s underlined and find variable for it Find equation that is for that variable Read equation like sentence (may need to look up what other variables man in the equation) Answer or solve the problem (if problem, use 4 steps for problem solving) Ex: “What is work?” Ex: W = Work Ex: W = Fd Ex: Work is force multiplied by distance

Use steps to solve To calculate the momentum of a pickup truck with a velocity of 25 m/s east, it is also necessary to know which of the following?  A.time elapsed  B.drive force of the motor  C.mass of the pickup truck  D.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 that momentum is mass x velocity, so… Use formula sheet to find what Momentum is: p =mv A 600 g basketball, a 57 g tennis ball, a 46 g golf ball, and a 2.7 g table tennis ball are moving with the same velocity. Which ball has the greatest momentum?  A.golf ball  B.basketball  C.tennis ball  D.table tennis ball If all have same velocity, then one with the biggest mass would give the biggest momentum (multiplying by the biggest number)

Use steps to solve What is the momentum of a metal disc with a mass of 1.5 kg sliding on a frictionless surface at 0.75 m/s?  A.0.50 kg • m/s  B.0.85 kg • m/s  C.1.1 kg • m/s  D.2.0 kg • m/s

4 steps for problem solving (calculations) • – 1. Write the equation (for what underlined) – 2. Replace the known values (everything with units and numbers- circle these when read problem) (Not all values are what you want- check with the equation from step 1) – 3. Solve the problem -- 4. Label with the correct unit of measurement.

Use steps to solve What is the momentum of a metal disc with a mass of 1.5 kg sliding on a frictionless surface at 0.75 m/s?  A.0.50 kg • m/s  B.0.85 kg • m/s  C.1.1 kg • m/s  D.2.0 kg • m/s Use formula sheet to find what Momentum is: p =mv

Use steps to solve What is the momentum of a metal disc with a mass of 1.5 kg sliding on a frictionless surface at 0.75 m/s?  A.0.50 kg • m/s  B.0.85 kg • m/s  C.1.1 kg • m/s  D.2.0 kg • m/s

What happens to the cart’s speed when the block lands in it? Must remember that momentum is conserved! What you start with is what you end with. What happens to the cart’s speed when the block lands in it? mv before = mv after 3. The diagrams below show a cart moving with a velocity, V, on a frictionless surface as a wooden block is being dropped. The block then falls straight down onto the moving cart. Which of the following statements describes what will happen after the block lands on the moving cart?  A.The cart will move to the left at a velocity less than the original velocity of the cart.  B.The cart will move to the left at a velocity greater than the original velocity of the cart.  C.The cart will move to the right at a velocity less than the original velocity of the cart.  D.The cart will move to the right at a velocity greater than the original velocity of the cart. mV = M___ v If mass increases, then speed must decrease in order for momentum to be conserved!

Can use conservation of momentum law to solve momentum collision problems p before = p after mv before = mv after

A 1 kg block sliding to the right on a level, frictionless surface with a speed of 2 m/s collides and sticks to a second 1 kg block sliding to the left. After the collision, the blocks are motionless. What was the speed of the second 1 kg block before the collision?  A.1 m/s B.2 m/s C.3 m/s D.4 m/s p before = p after mv1 + mv2 = 0 1x2 + 1x v = 0 It’s a collision, and they give us the velocity and mass, so we know it going to be a conservation of momentum problem 2 + v = 0 v = -2

Summarizer Write in notes What two things determine momentum?