science 20 unit b changes in motion students will describe

Name: __________________________________

Science 20 – Unit B – Changes in Motion

Science 20

Unit B – Changes in Motion

General Outcome 2: Students will describe and analyze the law of conservation of

momentum for one-dimensional collisions and change in momentum (impulse) to

explain how force affects motion.

Specific Outcome 2.1sts: Explain the goal of technology is to provide solutions to

practical problems

Specific Outcome 2.6: Apply Newton’s third law of motion to explain the

interaction between two objects

Specific Outcome 2.2: Apply the law of conservation of momentum to one-

dimensional collisions and explosions

Specific Outcome 2.7: Relate, quantitatively, potential and kinetic energy to

work done

Textbook pages 257 – 281

Automobile technology has evolved to solve practical problems.

Automobile Technology

of the Past

Automobile Technology

of the Present

How the Change in Technology

Helped Reduce Injury metal front and rear

bumpers welded solidly to

the main frame of the

automobiles

large plastic bumpers

attached through shock

absorbers to a collapsible

frame

increased the time of the impact

between the vehicle and the

obstacle, reducing the force

required to stop the vehicle

solid metal frame collapsible frame with

crumple zones


between the vehicle and the

obstacle, reducing the force

required to stop the vehicle

metal dashboard, hard

plastic steering wheel

solidly attached to steering

mechanisms of the

automobile

padded dashboard and

interior with a collapsible,

shock-absorbing steering

wheel


between the occupants and the

interior of the vehicle, reducing the

force required to stop the

occupants

no seat belts or air bags seat belts and driver- and

passenger-side air bags;

often side-impact air bags


between the occupants and the

interior of the vehicle, reducing the

force required to stop the

occupants

seat belts: spread the force

needed to decelerate occupants

over the larger, stronger parts of

the body—the pelvis, chest, and

shoulders

seat belts: keep occupants in their

vehicles during a crash

Name: __________________________________


Sum of momentum before = sum of momentum after

TYPES OF COLLISIONS

There are three types of collisions that are involved when a vehicle is involved in a

collision.

PRIMARY COLLISION: occurs when a vehicle collides with another object, such as a

vehicle

SECONDARY COLLISION: occurs when the occupant collides with the interior of the

vehicle

TERTIARY COLLISION: occurs when the occupant’s internal organs collide within the

occupant’s body.

NEWTON’S THIRD LAW OF MOTION

Newton’s third law of motion states that whenever one object exerts a force on a

second object, the second object exerts an equal but opposite force on the first

object.

�⃗⃗� 𝟏 𝒐𝒏 𝟐 = �⃗⃗� 𝟐 𝒐𝒏 𝟏

CONSERVATION OF MOMENTUM

The Law of Conservation of Momentum states that if the net force acting on a system is

zero, the sum of the momentum before an interaction equals the sum of the

momentum after the interaction.

∑𝑝 𝑏𝑒𝑓𝑜𝑟𝑒 = ∑𝑝 𝑎𝑓𝑡𝑒𝑟

patriots-in-motion.wikispaces.com

Name: __________________________________


There are 3 different types of collisions that follow the law of conservation of

momentum.

physics.tutorvista.com

𝑚1𝑣 1 + 𝑚2𝑣 2 = (𝑚1 + 𝑚2)𝑣 1 𝑎𝑛𝑑 2

Hit and stick

www.physicsclassroom.com

Hit and rebound

𝑚1𝑣 1 + 𝑚2𝑣 2 = 𝑚1𝑣 ′1 + 𝑚2𝑣 ′2

www.kwantlen.ca

Explosion

(𝑚1 + 𝑚2)𝑣 1 𝑎𝑛𝑑 2 = 𝑚1𝑣 ′1 + 𝑚2𝑣 ′2

Name: __________________________________


Example 10

A 10 000 kg freight car travelling west with a velocity of 1.5 m/s collides with a 20 000 kg

freight car at rest. After the collision, the freight cars stick together. Determine the

velocity of the freight cars after the collision.

Because the objects are locked

together, they can be treated as

one object.

Name: __________________________________


Example Problem 11

A 3.0 kg ball rolling east with a velocity of 1.5 m/s collides with another 6.0 kg ball at rest.

After the collision, the first ball rebounds and is travelling at a velocity of 0.50 m/s[W].

a. Determine the velocity of the second ball after the collision.

b. Determine the momentum values of the balls before and after the collision.

a.

b.

Name: __________________________________


Example Problem 12

A 0.020 kg firecracker at rest explodes into two pieces. If a 0.015 kg piece flies off to the

right at a velocity of 3.00 m/s, determine the velocity of the other 0.0050 kg piece.

Name: __________________________________


mass g = 9.81 m/s2

height above reference point

DESIGNING HELMETS

Momentum, force, collisions, and energy are all considered when designing helmuts.

WORK is the transfer of energy from one object or system to another when a force is

applied over a distance.

𝑾𝒐𝒓𝒌 = 𝑭𝒐𝒓𝒄𝒆 × 𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆

𝑾 = �⃗⃗� × 𝒅

Work is measured in joules (J).

ENERGY is the ability to do work. Energy is measured in joules(J). since both work and

energy are measured in joules, work can be related to energy.

LAW OF CONSERVATION OF ENERGY states that when energy is changed from one form

to another, the total energy of the system remains the same.

GRAVITATIONAL POTENTIAL ENERGY is energy due to the position of an object above

Earth’s surface.

𝑬𝒑(𝒈𝒓𝒂𝒗) = 𝑾

𝑬𝒑(𝒈𝒓𝒂𝒗) = 𝑭 × ∆𝒅

𝑬𝒑(𝒈𝒓𝒂𝒗) = 𝒎𝒈𝒉

KINETIC ENERGY is energy due to the motion of an object.

𝐸𝑘 =1

2𝑚𝑣2

Name: __________________________________


Example Problem 13

An egg test dummy is fitted with a helmet and sealed in a plastic bag. The mass of the

egg, helmet, baggie, and paper clamp is 0.085 kg. The egg and its accessories are

attached to the swing and pulled back so that they are now 0.40 m above the

reference level. The egg is released and swings down to collide with a cement block.

a. Calculate the gravitational potential energy of the egg and its accessories.

b. Determine the kinetic energy of the egg and its accessories when it collides with

the cement block. Explain how this energy is transformed in the collision.

c. Calculate the speed of the egg and its accessories the moment before impact.

d. Calculate the magnitude and direction of the momentum of the egg and its

accessories just before impact.

e. Assume the egg and its accessories stop immediately after impact. Use this

information to approximate the change in momentum of the bag and its

contents.

f. Calculate the impulse required to stop the bag during impact.

g. If the impact lasts for 0.040 s, determine the force that acted upon the bag and

its contents during the collision using the equation for impulse.

h. Determine the acceleration of the egg and its accessories over the 0,040 s.

i. Use Newton’s second law to confirm your answer to question g, by calculating

the force that acted on the bag and its contents.

Name: __________________________________


Name: __________________________________


Practice questions:

Page 270 #17-19

Name: __________________________________


Name: __________________________________


Page 217 # 20

Name: __________________________________


Page 277 # 23-24

Name: __________________________________


science 20 unit b changes in motion students will describe

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