thursday honors ps. homework pg 369 problems 22-27
TRANSCRIPT
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Thursday Honors PS
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Homework
• Pg 369
• Problems 22-27
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Leading Ideas
• Newton’s 1st law
• Newton’s second law
• Weight = mass x 10 (9.8)
Difference between mass and weight
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To find the weight of an object
• Weight = mass x acceleration of gravity
• On Earth: acceleration due to gravity is equal to about 10 (9.8)
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Mass and Weight
• Mass:– Amount of stuff– Unchanging– Measure of Inertia– kg
• Weight:– Force of gravity– Changes because of location– N
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Answers to homework
• 22) 10 m/s2
• 23) 23 N• 24) 2.1 kg• 25) .04 m/s2
• 26) 15 N• 27) 43.75 N• 28) 3.7 N• 29) 58.5 N
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Additional Problems
• A 2.5 kg hula hoop is pushed forward with a force of 45.9 N. What is it’s acceleration?
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Answer
• F = ma
• F = 45.9 N m = 2.5 kg
• A = 45.9 / 2.5 = 18.4 m/s2
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Make up a problem
• Object : _______________
• Amount of net force: __________
• Mass of object: ____________
• Solve for acceleration
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Example problem
• A 1540 kg car starts from rest and accelerates to 50.7 m/s in 13.8 seconds. What is the net force on the car that causes this acceleration?
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Answer
• 1540 kg = mass• Rest = 0 m/s = initial velocity• 50.7 m/s = final velocity• 13.8 sec = time
• Want net force, but need to find acceleration
a = (vf- vi) / t then Fnet = ma
a= 3.7 m/s2 Fnet = 5700 N
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New homework Handout #3
• Working with Newton’s 2nd Law• Review conversions, acceleration
• All questions are in book• Pg 852 3,4• Pg 857 89-95
• To be handed in on Monday
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Newton’s third Law
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3rd Law
• For every _____________
There is an __________ but opposite
__________.
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• For every action there is an equal and opposite reaction
• Forces come in pairs– Equal in size– Opposite in direction– Applied to different objects
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Examples of 3rd law
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Actions that can be related to 3rd law in the classroom
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If all forces are equal and opposite, how does anything
move?
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Answer
• Though equal in size, the forces act on different objects
Force of ground on box
Force of box on ground
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Trebuchet
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To change the motion of something
• Need to have a net force (unbalanced forces) on the object in order to change its motion
Force of rope on box
Friction force
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Free Body Diagrams
• Represent the object by a simple geometric shape or a dot
• Represent all forces on that object by arrows that originate from shape/dot
• Only represent the forces that are applied to the object, NOT forces the object applies to other things
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What would be the free body diagram of …..
• What are the forces on the dog?
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Answer
Dog
Applied force of ground pushing paws forward
Reactive force of ground
Force of leash
Weight of dog
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Create a free-body diagram of one of the dancers
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Create a free-body diagram of the ball
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• Draw a free-body diagram of the rock climber