DAY 49
NGSS Standard (this is what we're learning with this unit)
Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship amongthe net force on a macroscopic object, its mass, and its acceleration. [Clarification Statement: Examples of data could include tables or graphs of position or velocity as a function of time for objects subject to a net unbalanced force, such as a falling object, an object sliding down a ramp, or a moving object being pulled by a constant force.] [Assessment Boundary: Assessment is limited to one-dimensional motion and to macroscopic objects moving at non-relativistic speeds.]
#GOALS: SWBAT....
1. Use FBD's to find Net Force, mass, acceleration
2. Use mu and Fn to find Ff.
3. Explain the relationship between mass, Fn, and the behavior of a horizontally moving object
WARM-UP (4 minutes)
A rightward force is applied to a 5-kg object to move it across a rough surface with a rightward acceleration of 2 m/s2. The coefficient of friction between the object and the surface is 0.1. Use the diagram to determine the gravitational force, normal force, applied force, frictional force, and net force. (Neglect air resistance.)
Answers to the warm up are at the bottom of this page. Allllllll the way at the bottom.
CLASSWORK
1. 049A: Practice Problem (4 minutes)
A rightward force of 25 N is applied to a 4-kg object to move it across a rough surface with a rightward acceleration of 2.5 m/s/s. Use the diagram to determine the gravitational force, normal force, frictional force, net force, and the coefficient of friction between the object and the surface. (Neglect air resistance.)
Answers to the warm up are at the bottom of this page. Allllllll the way at the bottom.
2. 049B: Newton's Second Law Concept Builder
- Quiz Monday on this skill
- Complete all 3 levels, all 10 FBD's, in your notes. You'll have approx 3 minutes per problem, so work efficiently.
- Click the "Check Answer" button for each box to check your work as you progress through each portion of the FBD.
- Be sure to write your FBD and answers prior to hitting "Check Answer" for the final box, as when you get all the info correct, the program will automatically
move you to the next problem, and you won't be able to navigate back.
- Questions?
- Help Me button
- Remind App
LEARNING AT HOME (HW)
049C: Have a fun and safe Halloween
NGSS Standard (this is what we're learning with this unit)
Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship amongthe net force on a macroscopic object, its mass, and its acceleration. [Clarification Statement: Examples of data could include tables or graphs of position or velocity as a function of time for objects subject to a net unbalanced force, such as a falling object, an object sliding down a ramp, or a moving object being pulled by a constant force.] [Assessment Boundary: Assessment is limited to one-dimensional motion and to macroscopic objects moving at non-relativistic speeds.]
#GOALS: SWBAT....
1. Use FBD's to find Net Force, mass, acceleration
2. Use mu and Fn to find Ff.
3. Explain the relationship between mass, Fn, and the behavior of a horizontally moving object
WARM-UP
A rightward force is applied to a 10-kg object to move it across a rough surface at constant velocity. The coefficient of friction between the object and the surface is 0.2. Use the diagram to determine the gravitational force, normal force, applied force, frictional force, and net force. (Neglect air resistance.) (hint: find Fg first, then Fn. Calculate Ff, then find Fa)
CLASSWORK
1. 049A: Rocket Sled (friction sim)
- handout/instructions: Read, then complete: LINK
- simulation activity: LINK
LEARNING AT HOME (HW)
- No new learning at home assignments tonight, however if you don't finish the classwork today, you'll need to finish it tonight.
- If you didn't do the assignments I checked in class (DAY 46: two hw videos; DAY 47: cw FBD's (20 of them); DAY 48: video HW), do them tonight for late (80% credit)
WARM-UP:
take a look at this chart. A. In this problem, what is the impulse always equal to? B. What happens to the force felt during the collision as the time of collision is increased?
Combinations of Force and Time Required to Produce 100 units of Impulse
C. If you're boxing, and you know you're going to get punched, would it make more sense to:
flex your neck muscles so your head doesn't move when you get hit.
relax your neck muscles so your head moves when you get hit.
D. Why?
You’re in a car collision. Which of the following scenarios would be safer for your body?
Not sure how to answer this question?
A. Find the change in velocity for Case A and Case B
B. For which case would the change in momentum, or impulse, be smaller? What does that tell you?
From the Flipping Physics video, what is the benefit of wearing a helmet during a collision?
CLASSWORK:
#049A: Impulse/Change in Momentum Practice
Complete problems 1-7 (all) in the Check your Understanding section here --> LINK
#49B:
A 240.0-kg snowmobile accelerates, which results in a force being exerted that speeds up the snowmobile from 6.00 m/s to 28.0 m/s over a time interval of 60.0 s.
A. Sketch the event, showing the initial and final situations.
B. What is the snowmobile’s change in momentum? What is the impulse on the snowmobile?
C. What is the magnitude of the average force that is exerted on the snowmobile?
A 2200-kg vehicle traveling at 94 km/h (26 m/s) hits a concrete wall. Suppose a 60kg person is driving the car. The velocity of the person equals that of the car both before and after the crash, and the velocity changes in 0.20 s. Sketch the problem.
a. What is the average force exerted on the person?
b. Some people think that they can stop their bodies from lurching forward in a vehicle that is suddenly braking by putting their hands on the dashboard. Find the mass of an object that has a weight equal to the force you just calculated. Could you lift such a mass? Are you strong enough to stop your body with your arms?
Learning at home (HW)
(4:21) Demonstrating How Helmets Affect Impulse and Impact Force - EDpuzzle
(3:59) Review of Momentum, Impact Force, and Impulse - EDpuzzle
Answers to Warm-Up
Y-Direction
Fnet y = 0 This means Fg and FN are equal and opposite
Fg=mg --> Fg = (5kg)(9.8m/s2) = 49N down
FN = 49N up
X-Direction
Accel x = 2m/s2 therefore, Fnet x = (5kg)(2m/s2), which means: Fa - Ff = (5kg)(2m/s2) So, find Ff using FN and you can find Fa
FN = mu * Fg = (0.1)(49N) = 4.9N
Plug that into Fa + Ff = 10N
Fa + -4.9N = 10N Fa=14.9N
Answers to Classwork 049A