DAY 38

#Goals: SWBAT...

1. Determine if mass can be cancelled from all terms in the equation

2. Determine if a scenario represents work

3. Solve work problems

***Warm up check for Day 30-38 (9 warm-ups total) will be Monday 03/05***

Warm-Up (4min): Did Everyone Bring Mass to the Party?

You have to be able to identify when mass cancels out of an equation.

Recall: The “equation” is the party and the individuals are the terms delineated by a subtraction, addition or equal sign.

Stuck? Confused? Check this LINK for help

Copy the equations below, then answer the question, which is: "Can mass be cancelled in the equation?" If it can, cancel it (show your work). If it can't, write why you can't cancel mass.

1. 0 = ma_x - F_f (assume F_N=F_g)
2. mgh + 1/2mv² = 4kx²
3. 1/2mv_i² = 1/2mv_f² + mgL(1− cosθ)
4. F_tension - F_g = ma_y

CLASSWORK

1. #038A: Building Your Problem Solving Skills

Recall: W = F • d • cos Θ where F is the force, d is the displacement, and the angle (theta) is defined as the angle between the force and the displacement vector.

Solve the following. Draw FBD's. Show all work. Include units and correct sigfigs.

I'll check your work Monday (03/05)

If you get stuck, or want to check your answers, there's a link to help in the Homework section below

Instructions: For each case, indicate which force(s) are doing work upon the object. Then calculate the work done by these forces.

A) A 10-N frictional force slows a moving block to a stop after a displacement of 5.0 m to the right.

B) A 10-N force is applied to push a block across a frictional surface at constant speed for a displacement of 5.0 m to the right.

C) An approximately 2-kg object is sliding at constant speed across a friction free surface for a displacement of 5 m to the right.

D) An approximately 2-kg object is pulled upward at constant speed by a 20-N force for a vertical displacement of 5 m.

3. Before beginning its initial descent, a roller coaster car is always pulled up the first hill to a high initial height. Work is done on the car (usually by a chain) to achieve this initial height. A coaster designer is considering three different incline angles at which to drag the 2000-kg car train to the top of the 60-meter high hill. In each case, the force applied to the car will be applied parallel to the hill. Her critical question is: which angle would require the most work? Analyze the data, determine the work done in each case, and answer this critical question.

4. Ben Travlun carries a 200-N suitcase up three flights of stairs (a height of 10.0 m) and then pushes it with a horizontal force of 50.0 N at a constant speed of 0.5 m/s for a horizontal distance of 35.0 meters. How much work does Ben do on his suitcase during this entire motion?

5. A force of 50 N acts on the block at the angle shown in the diagram. The block moves a horizontal distance of 3.0 m. How much work is done by the applied force?

6. How much work is done by an applied force to lift a 15-Newton block 3.0 meters vertically at a constant speed?

7. A student with a mass of 80.0 kg runs up three flights of stairs in 12.0 sec. The student has gone a vertical distance of 8.0 m. Determine the amount of work done by the student to elevate his body to this height. Assume that his speed is constant.

9. A tired squirrel (mass of 1 kg) does push-ups by applying a force to elevate its center-of-mass by 5 cm. Estimate the number of push-ups that a tired squirrel must do in order to do a approximately 5.0 Joules of work.

At Home Learning (HW)

1. Complete all problems from #038A

If you got stuck, answers and more help are here at this link: LINK

2. #038B: Monday we will cover Kinetic and Potential Energy: Watch/take notes/complete edPuzzles on the following:

1. (5:25) Introduction to Kinetic Energy with Example Problem - EDpuzzle
2. (5:48) Introduction to Gravitational Potential Energy with Zero Line Examples - EDpuzzle

3. Many of you had questions about how to solve the more advanced problems from the past couple days. I've posted youtube videos showing the solutions to those with the links below

Day 35 part 1/2 http://www.youtube.com/watch?v=W7q3Mkz4iOg

Day 35 part 2/2 http://www.youtube.com/watch?v=22TTMSiDAfw

Day 36 http://www.youtube.com/watch?v=IdClvsS4DN8

Also, if you're at all confused by the warm-up from yesterday, here's more info on that: http://www.physicsclassroom.com/mmedia/energy/au.cfm