You Must Show All Equations Used and Identify All Variables

Physicist______Investigational hour ______Chapter 8 HW #1 This homework really is WORK You must show all equations used and identify all variables. 1 (1). A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, which changes the momentum of that object. What do we call the quantity force x distance, and what quantity can this change?

2 (2). Work against gravity is required to lift a barbell. How many times more work is required to lift the barbell three times as high?

3 (3). Which requires more work against gravity, lifting a 100 N load a vertical distance of 2 m or lifting a 50 N load a vertical distance of 4 m?

4. A force of 8.0 x 102 N is needed to push a car across a lot. Libby Miller and Jacob Silasi, two Physics students, push the car 40. m. How much work is done? (3.2 x 104 J)

5. Using a pulley system Ella Hannah does 1920 J of work to lift a crate from one floor to the next in a warehouse. The force is exerted through a distance of 40. m on the rope of the pulley system. How much force was used to lift the crate? (48 N)

6. In order for Michelle Reingold to change a tire, a force of 80. N is exerted on the handle of a screw type bumper jack. The handle to which the steel shaft is attached has a radius of 0.50 m. The handle is turned through 30. revolutions. How much work is done? Hint - determine the distance it move in one revolution (d=2r) and then the total distance (7500 J) 7. Lauren Dresler and Luke Prescott use a force of 1760 N to push a piano weighing 8800 N up a 20. m ramp. a. How much work is done? (35,200 J)

b. The piano is being moved from street level to the second level. The second floor is 4.0 m above street level. If Lauren and Luke decide to lift the piano straight up using ropes, how much work would they do? (35,200 J)

8. Keith Lawrence uses a rope to pull a 1.0 x 103 kg boat 50. m along a wharf. The rope makes an angle of 45 degrees with the horizontal. If a force of 40. N is applied to the rope (only the horizontal component is used to move the boat), how much work is done against water friction? (1400 J)

9) Due to friction, a force of 4.0 x 102 N is needed for Alexis Camacho to drag a wooden crate across a floor. The rope tied to the crate is held at an angle of 56 degrees with the horizontal. a. How much tension is needed in the rope to move the crate? (720 N)

b. What work is done against friction if the crate is dragged 25 m? (10,000 J) Physicist______Investigational hour ______Chapter 8 HW #2 This homework shouldn’t take too much POWER You must show all equations used and identify all variables. 1 (5). How much power is required to do 1.0 x 102 J of work on an object in a time of 0.50 s? How much power is required in the same work is done in 1.0 s?

2. A box that weighs 1.0 x 103 N is lifted by Garrett Dahlke a distance of 20. m straight up by a rope and pulley system. The work is done in 10. s. What amount of power is used in watts and in kilowatts? (2000 W 2 kW)

3. An electric motor lifts a 2.0 x 103 kg elevator 18 m in 40. s. a. How much work is done? (350,000 J)

b. What is the power of the motor in watts and in kilowatts? (8800 W 8.8 kW) 4. How much work does a 4.0 x 102 watt motor do in 5.0 min.? (120,000 J)

5. Zac Wiliams, an overweight painter has a mass of 105 kg. On a typical workday he climbs a ladder to a vertical height of 7.0 m twenty-five times. If body fat has an energy value of 38 kJ/g what mass, in grams, could the overweight painter "work off" if Zac refrained from eating all day? Hint - determine the total distance UP the ladder he travels, then determine the work done against gravity (4.7 g) Physicist______Investigational hour ______Chapter 8 HW #3 Do I have enough POTENTIAL and KENETIC ENERGY to get this homework done? You must show all equations used and identify all variables. 1 (7). If Nikita Anand does 100 J of work against gravity to elevate a bucket of water, what is its gravitational potential energy (Eg) relative to its starting position?

2 (8). Olivia Tobias raises a boulder above the ground so that its potential energy (Eg) relative to the ground is 200 J. She waits until Mr. Vining is walking by then drops the boulder narrowly missing him. What is its kinetic energy (Ek) just before it hits the ground?

3 (9). Suppose an automobile driven by Abby McDonald has 2000 J of kinetic energy (Ek). When it goes at twice the speed, what will be its kinetic energy? What’s its kinetic energy at three times the speed?

4 (32). Does an object with momentum always have energy? Does an object with energy always have momentum? Explain.

5 (33). If a mouse and an elephant both run with the same kinetic energy (Ek), can you determine which is running faster? Explain in terms of the equation for EK.

6. The 200.-kg hammer of a pile driver is lifted 10. m. Find the potential energy (Eg) of the system when the hammer is at that height. ( 20,000 J) 7. A 60.-kg shell is shot from a cannon to a height of 400. m.

a. What is the potential energy (Eg) of the earth-shell system when the shell is at this height? (240,000 J)

b. What is the change in potential energy ( Ek) of the system when the shell falls to a height of 200. m? (120,000 J)

8. In order to charge the plates of a small storage battery, a Nick Nordqvist uses a hand generator that is cranked through a total distance of 250 m. An average force of 120 N is applied to the crank as it is turned. a. What is the total work done to charge the plates? (3.0 x 104 J)

b. If the work is done in one minute, what power is developed? (500 W)

c. The storage battery is then used to power a 10. watt light bulb. How many minutes can the bulb be used before the battery must be recharged? (50 min.) 9. a. A 10 kg mass moves with a speed of 20 m/s. Find its kinetic energy (Ek). (2000 J)

b. If the 10 kg mass moves with a speed of 10 m/s, what is its kinetic energy (Ek)? (500 J)

c. What is the ratio of the answer of A to that of B? Why? (4:1)

10) What is the kinetic energy (Ek) of a 1600-kg car driven by Hayden Arnold and Katelynn Lewallen which moves a. at 30. km/h? (5.5 x 104 J [hint don’t forget to convert to m/s])

b. at 60. km/h? (2.2 x 105 J)

c. What is the ratio of (b) to (a)? (4:1) Physicist______Investigational hour ______Chapter 8 HW #4 I have a feeling I’m going to need CONSERVE my ENERGY to get this homework done! You must show all equations used and identify all variables. 1 (15). Is it possible for a machine to multiply energy or work input? Does this violate the law of energy conservation?

2 (18). What is the efficiency of a machine that requires 100 J of input energy to do 35 J of useful work?

3 (20). What is the efficiency of Mr. Johnson when a he expends 650 W of power to deliver mechanical energy to the bicycle at the rate of 210 W?

4 (28). A lever is used to lift a heavy load. When a 50. N force pushes one end of the lever down 1.2 m, the load rises 0.20 m. Calculate the weight of the load.

5 (35). Most Earth satellites follow an oval-shaped (elliptical) path rather than a circular path around Earth. The Eg increases when the satellite moves farther from Earth. According to the law of energy conservation, does a satellite have is greatest speed when it is closest to or farthest from Earth? Why?

6 (36). Suppose you are at the edge of a cliff and throw one ball down to the ground below and another up at the same speed. The upward-thrown ball rises and then falls to the ground below. How do the speeds of the balls compare when striking the ground? Neglect air resistance and use the conservation of energy to arrive at your answer.

7 (37). Why does a small, lightweight car generally have better fuel economy than a big, heavy car? How does a streamlined design improve fuel economy?

8 (38). Does using an automobile’s air conditioner while driving increase fuel consumption? What about driving with the lights on? What about playing the car radio when parked with the engine off? Explain in terms of the conservation of energy. 9 (40). You tell your friend that no machine can possible put out more energy than is put into it, and your friend states that a nuclear reactor puts out more energy than is put into it. What do you say?

10. Kaylee Vanatta sees Mr. Vining on the street below and she pushes a 8.0 kg flower pot from a window ledge 12 m above the sidewalk. a. Complete the energy flow diagram for the scenario described above

Ek Eg Ek Eg Ediss

b. What is the K.E. of the pot just as it reaches the sidewalk? (940 J)

c. Using energy considerations only, determine the speed of the pot just before it strikes the walk. (15 m/s)

11. Consider a 5.0 kg mass held by Lena Soble 10. m above the earth's surface. She then drops the mass. Consider the energy of the mass after it has fallen 4.0 meters. a) Complete the energy flow diagram for the scenario described above

Ek Eg Ek Eg Ediss

b. What potential energy does the mass have? (490 J)

c) What is the change in potential energy over the 4.0 meters it fell? (-196 J) d. What kinetic energy does it have after it falls 4.0 m? Explain (196 J)

e. What speed does the mass have after it falls the 4.0 m? (assume it falls from rest...) (8.9 m/s)

12. Ky Silverman is out playing with a 15.0 kg model plane that flies horizontally at 12.5 m/s. a. Calculate its kinetic energy. (1170 J)

b. The plane goes into a power dive and levels off 20.4 m closer to the earth. Complete the energy flow diagram for this scenario.

Ek Eg Ek Eg Ediss

c. How much Eg did it lose during that time? (3000 J)

d. How much Ek did the plane gain during the dive? (3000 J)

e. What is its new kinetic energy? (4170 J)

f. Neglecting frictional effects, what is its new horizontal velocity? (23.6 m/s) 13. Joshua Hitt and Sydney Summer are out skating on a lake and they push on a 5.0 kg log to clear a skating area. a. If they do 6.0 x 102 J of work on the log and the ice is nearly frictionless, what speed do they give to the log? (15 m/s)

b. Sketch a picture depicting the situation and then sketch an energy bar graph for the initial and final situations. Use the energy flow diagram to indicate if work causes energy to enter or leave the system.

Ek Eg Ek Eg Ediss

14. A 1500 kg car on top of the of a 100. m hill rolls down the hill to Mr. Hill. The car loses 7.0 x 105 J of energy to friction.

a. Sketch a picture depicting the situation and then sketch an energy bar graph for the initial and final situations. Use the energy flow diagram to indicate if work causes energy to enter or leave the system.

Ek Eg Ek Eg Ediss

b. Calculate the speed of the car at the bottom of the hill. (hint- Ediss = energy loss to friction) (32 m/s) 15. You are at Six Flags Magic Mountain on the roller coaster Goliath and you can’t help but think about the physics involved. You determine that the height of the first hill is 84.0 m and the height of the second hill is 22.0 m. You ask one of the technicians what the mass of a full train would be and he tell you 750. kg. a. Determine how much gravitational potential energy the car would have at the top of the first hill (0.617 MJ)

b. Assuming that the car looses 60 500 J of energy to friction what is it Ek at the bottom of the first hill? (557 kJ).

c. What would its velocity be at the bottom of the first hill? (38.5 m/s)

d. Complete the energy flow diagram for moving from the top of the first hill to the top of the second hill (this is not a frictionless rollercoaster).

Ek Eg Ek Eg Ediss

e. Assuming that the car looses 80 500 J of energy to friction when it reaches the top of the second hill. What is it Ek at the top of the second hill? (375 kJ)

f. What would its velocity be at the top of the second hill? (31.6 m/s) Physicist______Investigational hour ______Chapter 8 Review I don’t have enough CONSERVED ENERGY – I need a POWER bar to get this WORK done. You must show all equations used and identify all variables.

1. An experimental roller coaster is shown below. It uses springs for both the launching and the braking mechanisms. Do the calculations necessary to complete the table below. The car’s mass is 1000.0 kg. The Ediss given is the total amount of energy that has changed from mechanical energy to thermal energy at that point.

Ee (J) Eg (J) Ek (J) Ediss(J) Total Energy Velocity (m/s) (J) A (before launch) B

Draw a bar chart for each point A-E

2. A grocery clerk has to lift a case of cans of vegetables (for the food drive of course) onto a cart. If the mass of the case is 8.0 kg and the cart is 0.75 m above the ground, how much work is done? 3. Early in the shift, the grocery clerk takes 1.5 seconds to lift the case into the cart; by the end of the shift it takes 2.2 seconds. Calculate the power generated in each case.

4. You pull your darling baby brother along on a sled as shown. How much work do you do as you pull the sled for 225 m along the street?

5. If it takes you 8.00 minutes to pull the sled, what power was generated?