Extra practice questions - Ch. 5

1.Choose a simple machine to could be used to do the following: A) lifting a car to change a tire; B) removing a lid from a can of paint; C) undoing a tight bolt; D) splitting a log for firewood; E) moving a car from the lower level of a parking garage to a higher level; F) raising a bucket of tools from the sidewalk to the second floor. 

2.Draw a labeled diagram of each class of lever that requires the LEAST amount of input force. 

3.A boy and a girl sat at opposite ends on an unusual see-saw in a playground. Suppose the total length of the see-saw is 3 m and assuming that the anchor point is 1/5 distance away from the girl. State the IMA in two ways. In what scenarios is it “easier” to lift the other up?  

4.To remove a screw, Jess uses a screwdriver. What simple machine is this? Suppose that the shaft of the screwdriver has a diameter of 0.8 cm and the handle has a radius of 1.6 cm, what is the IMA? 

5.Determine the IMA of a bicycle if the chain provides an input force to a back sprocket that has a radius of 8 cm and the back wheel of the bicycle has a radius of 32 cm. 

6.If the IMA of a first-class lever is 2 and the distance from the fulcrum to the load is 60 cm, how far away from the fulcrum is the input force? Draw a labeled diagram along with your calculation. 

7.If the IMA of a ramp is 12 and the length of the ramp is 4 m, what is the height of the ramp? Draw a labeled diagram along with your calculation.

8.A 12 kg crate is pushed up a 8 m ramp to reach a height of 4 m with a force of 100 N. What is the efficiency of the ramp?

9. You have to lift a mass to a higher location so that the mass gains 800 J of gravitational potential energy. You may use one of the three different mechanisms provided. Calculate the efficiency of each mechanism. Which one will you use? (A) You use an electric motor that requires 850 J of energy to lift the mass. (B) You pull the role of a pulley, which is attached to the mass, a distance of 6 m with a force of 150 N. (C) You push the mass 10 m up a ramp with a force of 140 N. 

Extra practice questions - Ch. 4

   1.Two books are dropped from different heights: Book A, with a mass of 450 g, is dropped from a height of 350 cm; Book B, with a mass of 300 g, is dropped from a height of 500 cm. Which book does more work? 

2.In a grade 8 classroom, five students demonstrate different amount of work done by doing different things. Tommy lifts a 4500 g object 50 cm up from the ground. Clare holds a 1kg object 50 cm over her head. Steven pushes a 10 kg box across the floor with a force of 70 N for a distance of 3.5 m. Jeff drops a 500 g mass from the desk top that sits 80 cm from the floor. And Kelly kicks a ball 8 m across the room with a force of 15 N. Order each student’s name from the least amount of work done to the greatest amount of work done. 

3.William pushes a cargo box up a 4 m ramp to load onto a platform that is 80 cm above the ground. The cargo has a mass of 30 kg. 

a.What is the IMA of using the ramp?

b.How much work needs to be done to lift just the cargo up?

c.How much work does William need to do through using the ramp if input force is 100N? 

4.If a person is required only a quarter amount of work because he’s using a machine, and the force of the load is 120 N, how much force does he need to put in? What is the mechanical advantage of this machine? 

Unit Outline

To help you prepare for the unit test, below is a outline of key vocabulary and concepts in the form of questions. Use your notes, quizzes, labs, worksheets to help you study.

4.1 - Understanding forces 
1. What is force?
2. How are forces classified? Provide examples for each.
3. What is mass? Weight? What is the proper unit for each? What's the relationship between mass and weight on Earth? How does this relationship change if you were on the moon?
4. Fg = mg 
5. When you plot a weight vs. mass graph, what does the slope of the line represent? If Planet X has a steeper slope than Planet Y, which planet has stronger gravitational strength?

4.2 - Work and Energy
1. What is work? What's the proper unit? What is energy? How is work related to energy?
2. Energy can be transferred or transformed. Provide an example of each.
3. How is kinetic energy different from potential energy?
4. How does friction 'do work'?
5. W = fd  

4.3 Mechanical Advantage
1. What is a machine?
2. Identify the 3 ways that machines help make our lives easier.
3. What is input force? What is output force?
4. MA = f out/ f in
5. Give an example of MA = 1
6. IMA = d in / d out
7. Is IMA >, < or = MA? Explain.
8. Explain why IMA < 1 may be desirable sometimes. Give an example.

5.1 Simple Machines
1. Identify the 6 simple machines.
2. Sketch the 3 different classes of lever. Provide a real-life example for each class.
3. Remember that the general formula for IMA is d in / d out, even though there are specific formulas for a lever, ramp, and wheel & axle. The important is knowing where is the input and where is the output.

5.2 Efficiency
1. Efficiency is about saving energy...the more efficient the machine, the less friction it has and therefore less heat is produced (i.e. less wasted energy).
2. Input work > output work. WHY?
3. Efficiency = W out / W in x 100%
4. What are some ways to increase efficiency?

Update (unit test date set)

This week's focus - 

Labs: Measuring MA and IMA of simple machines

[Guiding questions: How do MA and IMA compare in a first-class lever? What about an inclined plane? What do the differences in MA and IMA mean? What does this mean about a lever and a ramp?]

Quiz alert! 

Be ready...there will be one this week about levers and MA and/or IMA calculations. 

Unit Test is set on Thursday, Feb. 27, and Friday, Feb. 28 (Day 1). 

[It'll be a 2-part test; one part each day.]

Update

CH. 4 - complete (chapter quiz has been marked and returned)

Focus this week: 5.1 Simple Machines and Mechanisms
Main concepts:
*6 simple machines - lever, pulley, wheel & axle, inclined plane, screw, and wedge
*3 classes of lever - classification depends on where the Fin, Fout, and fulcrum are
*calculating IMA of lever, wheel and axle, and inclined plane - underlying formula is still
IMA = d in / d out
*IMA of a pulley - count the # of supporting ropes

Next week: lab (Determining the IMA of simple machines) and quiz on 5.1