Unit 6 review

Unit 6 review

by Israel Hinojosa

Momentum ​

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• Momentum is “inertia in motion.”

• Momentum is represented by “p”.

• Momentum is the product of the mass and the velocity of an object. 

                             p = mv

• Momentum is a vector quantity, meaning it has both magnitude and direction. Its direction is the same as its velocity.

Solving for velocity

​Velocity is distance over time

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​v=d/t

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​Some problems will make you find the velocity first before finding momentum

​Weight vs. Mass

​When solving for momentum we use mass, but sometimes they give us weight instead.

• ​Mass is matter in an object.

• ​Weight is the mass multiplied by the gravity being applied to the object.​

​Converting weight to mass

• Mass is in kg

• ​Weight is in N

• ​converting N to kg - take the Weight (N) and divide by gravity (9.8)

Multiple Choice

A 4000 kg car travels at a velocity of 52.5 m/s. What is the momentum of the car? $$p=mv$$  

• 210000 kgm/s

• 76.19 kgm/s

• 4052.5 kgm/s

• 3947.5 kgm/s

Multiple Choice

Based on your knowledge of momentum, if you need to stop these two animals, who will be harder to stop- a 6 Kg mouse running at 7.5 m/s or a 20 Kg cat running at 3.2 m/s? Prove your answer mathematically. $$p=mv$$  

• the cat because it has a momentum of 150

• the cat because it has a momentum of 64

• the mouse because it has a momentum of 45

• the mouse because it has a momentum of 120

Multiple Choice

A bicyclist is riding his bike around town. He goes a distance of 800 m in 115 s. If the cyclist has a mass of 89 kg, what is his momentum while riding?

• 1033.7 kgm/s

• 619.1 kgm/s

• 10235 kgm/s

• 47200 kgm/s

Fill in the Blanks

A dart with a weight of 0.61 N is thrown at a velocity of 28.3 m/s. What is the momentum of the dart? Round to the nearest hundredths place

​Impulse

Multiple Choice

A 52 kg marathon runner is nearing the finish line in a marathon. She is running at a velocity of 4m/s until she sees the finish line then she picks up the pace to a velocity of 7m/s. What is the Impulse (change in momentum) of the runner?

$$\Delta p=mv_f-mv_i$$  

• 208 Ns

• 29.7 Ns

• 13 Ns

• 156 Ns

Fill in the Blanks

Ann pushed on a 10 kg shopping cart with a force of 60 N for 4.5 seconds. (a) Find the impulse applied to the cart. (b) How fast did the cart go if it was initially at rest?

$\Delta p=mv_f-mv_i\ \parallel\ \Delta p=F\times t$  

​Conservation of Momentum

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• The total momentum of a system of objects must remain constant, unless outside forces act upon the system.

• Momentum cannot be created nor destroyed.

• ​Momentum can be transferred from one object to another

​Types of Collisions

​Elastic Collisions- Collisions where the objects bouce off each other. Objects have their own masses and velocities.

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Inelastic Collisions- Collisions where objects collide and get stuck together. Objects that get stuck move as one after the collision. The masses are combined for these objects.

​Equations for Conservation of Momentum

​Elastic Collision

​m_Av_Ai + m_Bv_Bi = m_Av_Af + m_Bv_Bf

​Inelastic Collision

m_Av_Ai + m_Bv_Bi = (m_A + m_B) x v_f

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Fill in the Blanks

What is the final velocity of the car and truck after the crash. They get stuck so this is inelastic.

m_Av_Ai + m_Bv_Bi = (m_A + m_B) x v_f

Fill in the Blanks

Car A with a mass of 1200 kg is driving down the highway at a velocity of 32m/s. Car B with a mass of 1500kg comes from behind at a velocity of 46m/s and rear ends car A. After the collision Car A is now traveling at a velocity of 42 m/s. What is the velocity of car B after the collision?

​m_Av_Ai + m_Bv_Bi = m_Av_Af + m_Bv_Bf