PHYS 125 S01 F24 Lecture 03 PDF

PHYS 125 Friday, September 13, 2024 Lecture Week 3 ANNOUNCEMENTS HW 3: due next Thursday (September 19) on Canvas...

PHYS 125 Friday, September 13, 2024 Lecture Week 3 ANNOUNCEMENTS HW 3: due next Thursday (September 19) on Canvas PHYS 125 - Week 2 15  Women’s powerli.ing at the Olympics 2024 Week 3 Topics A. Kinematics in 2D B. Newton’s three laws C. Catalogue of Forces D. Forces & Motion Learning Goals Understand the laws of nature that govern why objects move, don’t move, or experience a change in their motion. Learn to interpret how different types of forces act on objects. Learn strategies for approaching problems with forces and motion. Textbook readings Chapters 5.1-5.7, 6.1-6.4, 6.6, 7.1-7.5 PHYS 125 - Week 3 16 A. Kinematics in 2D PHYS 125 - Week 3 17  Concept Question: 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, where should you aim the arrow to ensure that it will hit the can? A. Slightly above the can B. Directly at the can C. Slightly below the can PHYS 125 - Week 2 18  Example: Solving a 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, prove the answer from the previous slide about where you should aim the arrow to ensure that it will hit the can. PHYS 125 - Week 2 20 D. Forces & Motion PHYS 125 - Week 3 28  D. Forces & Motion: How to read a word problem In the powerlifting final, an Iranian athlete sets the Paralympic record and wins Gold by lifting a 252 kg barbell. While he is in the process of lifting the barbell, his arms move at a constant speed. (a) What force is the athlete applying to the barbell? (b) What normal force is the barbell applying to the athlete’s hands? Men’s powerli.ing final at the Paralympics 2024 PHYS 125 - Week 3 29  D. Forces & Motion: How to read a word problem In the powerlifting final, an Iranian athlete sets the Paralympic record and wins Gold by lifting a 252 kg barbell. While he is in the process of lifting the barbell, his arms move at a constant speed. (a) What force is the athlete applying to the barbell? (b) What normal force is the barbell applying to the athlete’s hands? Men’s powerli.ing final at the Paralympics 2024 PHYS 125 - Week 3 30 C. Catalogue of Forces PHYS 125 - Week 3 31  C. Catalogue of Forces: Frictional Force Contact force? Agent: Conditions: Static friction: Kinetic friction: PHYS 125 - Week 3 32 C. Catalogue of Forces: Frictional Force PHYS 125 - Week 3 33  C. Catalogue of Forces: Tension Force Contact force? Agent: Conditions: PHYS 125 - Week 3 34 D. Forces & Motion PHYS 125 - Week 3 35  Example: How to approach an inclined plane problem A block of mass m is at rest on an ramp with angle θ and a coefficient of static friction μs with the block. PHYS 125 - Week 3 37  Example: How to approach an inclined plane problem A block of mass m is at rest on an ramp with angle θ and a coefficient of static friction μs with the block. PHYS 125 - Week 3 38  Example: How to approach an inclined plane problem A block of mass m is at rest on an ramp with angle θ and a coefficient of static friction μs with the block. PHYS 125 - Week 3 39  Example: How to approach an inclined plane problem A block of mass m is at rest on an ramp with angle θ and a coefficient of static friction μs with the block. PHYS 125 - Week 3 40  Concept Question: Friction on an incline During Kayak Cross, the athletes start by sliding down a 6 m long incline into the water. Each athlete has applied a different amount and type of waxed coating to their boat, such that their boats have different coefficients of kinetic friction with the ramp’s surface: Green athlete: μk = 0.20 Blue athlete: μk = 0.07 Red athlete: μk = 0.10 Yellow athlete: μk = 0.03 Which athlete has the largest acceleration down the incline? Men’s Kayak Cross at the Summer Olympics 2024 A) The green athlete. B) The red athlete. C) The blue athlete. D) The yellow athlete. E) The acceleration will be the same. PHYS 125 - Week 3 41  Example: Solving a force problem with tension A 60 kg climber attached to a safety rope with a tension of 288 N has made it to the top of a 15 m climbing wall. What is her acceleration when she lets go of the wall? (Assume upwards is the positive direction). Women’s speed climbing at the Olympics 2024 PHYS 125 - Week 3 43  EXTRA PRACTICE Suggested extra topics to review & questions to guide you to think deeper PHYS 125 - Week 3 46  Extra Practice: 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, where should you aim the arrow to ensure that it will hit the can? A. Slightly above the can B. Directly at the can C. Slightly below the can d i f th e c a n a v e c h a n g e s p r o b l e m h e a r r o w to w o u l d t h i y o u a i m th How W h e r e s h o u l d n ? o t f a l l ? i o n a r y ca does n i t w i l l h i t th e s ta t ensu r e PHYS 125 - Week 2 47 Extra Practice: Connecting Newton’s laws to projectile motion When we first learned projectile motion, we made the following statements without proof: The component of motion in the horizontal direction is “uniform motion,” with zero acceleration. The component of motion in the vertical direction is “free fall,” with acceleration due to gravity. Now, given what we’ve learned about Newton’s laws and drawing free body diagrams, can you prove why the above statements are true about projectile motion? Use the following scenario from last week’s slide set: A long jump athlete jumps with an initial velocity of 10 m/s at a takeoff angle of 60 degrees. PHYS 125 - Week 3 48  Extra Practice: Coordinate systems A block of mass m is at rest on an ramp with angle θ and a coefficient of static friction μs with the block. o d y d i a g r a m l d th e fr e e b l e , h o w w o u a te s y s te m s e xa m p a c o o r d i n For thi a d i n s te a d u s e d n g e i f w e h t t i l te d ? c h a that was n o PHYS 125 - Week 3 49  Extra Practice: Incline angles A block of mass m is at rest on an ramp with angle θ and a coefficient of static friction μs with the block. s i n s i d e th e e ta a p p e a r i n e a n g l e th th e fo r c e The in c l e c o m p o s e e u s e d t o d tr i a n g l e w v e c to r. o f g ra vi t y o v e h o w w e c a n y o u p r o m e tr i c a l l y, a n g l e ? G e r e th e s a m e w t h o s e a kno PHYS 125 - Week 3 50  ANSWERS TO LECTURE QUESTIONS Examples Concept Questions Try working through the questions on your own before checking the following slides! PHYS 125 - Week 3 51  Concept Question: 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, where should you aim the arrow to ensure that it will hit the can? A. Slightly above the can B. Directly at the can C. Slightly below the can PHYS 125 - Week 2 19  Example: Solving a 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, prove the answer from the previous slide about where you should aim the arrow to ensure that it will hit the can. PHYS 125 - Week 2 19  Example: Solving a 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, prove the answer from the previous slide about where you should aim the arrow to ensure that it will hit the can. PHYS 125 - Week 2 20  Example: Solving a 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, prove the answer from the previous slide about where you should aim the arrow to ensure that it will hit the can. PHYS 125 - Week 2 21  Example: Solving a 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, prove the answer from the previous slide about where you should aim the arrow to ensure that it will hit the can. PHYS 125 - Week 2 22  Example: Solving a 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, prove the answer from the previous slide about where you should aim the arrow to ensure that it will hit the can. PHYS 125 - Week 2 23  Example: Solving a 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, prove the answer from the previous slide about where you should aim the arrow to ensure that it will hit the can. PHYS 125 - Week 2 24  Example: Solving a 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, prove the answer from the previous slide about where you should aim the arrow to ensure that it will hit the can. PHYS 125 - Week 2 25  Example: Solving a 2D Two Body Problem There’s a new carnival game at the Houston Rodeo in which you must hit a metal can with a magnetic arrow. What’s the catch? Well, at the exact instant that you launch the arrow, this releases the can and it falls straight downwards. Knowing this, and neglecting air resistance, prove the answer from the previous slide about where you should aim the arrow to ensure that it will hit the can. PHYS 125 - Week 2 26  Concept Question: Friction on an incline During Kayak Cross, the athletes start by sliding down a 6 m long incline into the water. Each athlete has applied a different amount and type of waxed coating to their boat, such that their boats have different coefficients of kinetic friction with the ramp’s surface: Green athlete: μk = 0.20 Blue athlete: μk = 0.07 Red athlete: μk = 0.10 Yellow athlete: μk = 0.03 Which athlete has the largest acceleration down the incline? Men’s Kayak Cross at the Summer Olympics 2024 A) The green athlete. B) The red athlete. C) The blue athlete. D) The yellow athlete. E) The acceleration will be the same. PHYS 125 - Week 3 42  Example: Solving a force problem with tension A 60 kg climber attached to a safety rope with a tension of 288 N has made it to the top of a 15 m climbing wall. What is her acceleration when she lets go of the wall? (Assume upwards is the positive direction). Women’s speed climbing at the Olympics 2024 PHYS 125 - Week 3 44