Force and Motion Test 2 Review

Transcription

1 Force and Motion Test 2 Review Name: S8P5a. Investigate and explain that electric currents and magnets can exert force on each other. 1. What happens to a compass needle when it is placed next to a wire with electricity running through it? a. The needle spins around and around. b. The needle continues to point north. c. The needle points towards the wire. d. The needle rotates 180 and points south. 2. How, essentially, is the majority of electricity in the United States generated?? a. Solar power. b. Batteries. c. A magnet spins in a coil of wire. d. Atoms are smashed together until they fuse together. 3. Why would you use an electromagnet to lift scrap metal instead of a permanent magnet? a. It weighs less than a permanent magnet. b. It isn t quite as strong as a permanent magnet. c. It is cheaper than a permanent magnet. d. It can be turned on and off unlike a permanent magnet.

2 S8P5b. Demonstrate the advantages and disadvantages of series and parallel circuits and how they transfer energy. 4. Batteries can be made using potatoes though they produce very low voltage. How could you wire a bunch of them so that the voltage could be increased to a usable level? a. Connect them in Series. b. Connect them in Parallel. c. Connect them in a combination of Series and Parallel. d. Connect them all individually to the device you want to power. 5. In the circuit pictured to the right, which bulb or bulbs will stay lit if bulb C goes out? a. Bulb A b. Bulb B c. Bulbs A & B d. None of the bulbs 6. In the circuit pictured to the right, which bulb or bulbs will stay lit if Bulb A goes out? a. Bulb B b. Bulb C c. Bulbs B & C d. None of the bulbs

3 SPS10b. Explain the flow of electrons in terms of alternating and direct current; the relationship between voltage, current and resistance; and simple series and parallel circuits. 7. How much voltage would be produced in a circuit that contains a bulb with a resistance of 3Ω and a current of 6 amps? a. 0.5 volts b. 2 volts c. 9 volts d. 18 volts 8. A 9V battery is attached to a circuit carrying 12 amps of current and has a small electric motor attached. How much resistance does the motor have? a. 3Ω b. 0.75Ω c. 1.33Ω d. 108Ω 9. A lamp is plugged into a 120V wall outlet. The lamp s bulb has a resistance of 8Ω. How much current is there in the system? a. 15 amps b. 0.07amps c. 960amps d. 112amps

4 SPS8a. Calculate velocity and acceleration. 10. Chandler hikes 5 miles to a waterfall on the western side of a mountain in a half hour. What is his velocity? a. 6 miles per hour. b. 10 miles per hour west. c. 150 miles per hour west. d miles per hour east. 11. In a summer storm the wind is blowing with a velocity of 8 m/s north. Suddenly within 3 seconds the wind is blowing at 23 m/s north. What is the wind s acceleration? a. 552 m/s 2 b m/s 2 c m/s 2 d. 5 m/s A car accelerates from rest (zero velocity) to a speed of 36 m/s in 12 seconds. Calculate the acceleration. a m/s 2 b. 3 m/s 2 c. 24 m/s 2 d. 432 m/s 2

5 S8P3C. Demonstrate the effect of simple machines (lever, inclined plane, pulley, wedge, screw and wheel & axle) on work. SPS8e. Calculate amounts of work and mechanical advantage using simple machines. 13. Simple machines a. Reduce the amount of work required b. Increase the amount of work required c. Have no effect on the amount of work required. d. Don t work at all. 14. You apply a force on a crowbar to open a stuck door. The effort length of the crowbar is 24 cm long and the resistance length is 4 cm long. What is the mechanical advantage of the crow bar? a b. 6 c. 96 d. 28

6 15. A worker uses a board that is 4m long to pry up a boulder. A small rock is used as a fulcrum and is placed 0.5m from the resistance end of the lever. Calculate the mechanical advantage of the lever. a. 2 b. 3.5 c. 7 d A 15 meter ramp lifts object to a height of 2.5 meters. What is the mechanical advantage of the ramp? a b. 6 c d A ramp with a mechanical advantage of 8 lifts objects to a height of 1.5 meters. How long is the ramp? a b. 6.5 c. 9.5 d. 12

7 18. What is the mechanical advantage of the pulley system pictured to the right? a. 4 b. 5 c. 6 d What is the mechanical advantage of the wheel and axle in the picture to the right? a. 1 b. 4 c. 5 d How much work is required to move a 500N rock 6 meters? a. 83.3J b. 3000J c. 494J d. 506J

8 Answers & Explanations 1. The correct answer is C. When electric current passes through a wire it generates a magnetic field. The compass needle will then be attracted to the wire rather than the magnetic North Pole of the Earth. Turn off the current and the needle will once again point North. Hans Christian Oersted first discovered and documented this phenomenon. 2. The correct answer is C. Michael Faraday first discovered this phenomenon. The way you spin the magnet is linked to the energy sources we use. Mostly steam is generated which turns a turbine which in turn spins the magnet. 3. The correct answer is D. Permanent magnets have a set strength. Electromagnets can be strengthened or weakened by adjusting the amount of current in the wire and the number of coils in the wire. With a permanent magnet you have to actively remove things that are attracted and stuck on the magnet. With an electromagnet you just turn it off and the metal will fall costing you no effort or energy. 4. The correct answer is A. With series circuits, voltages are added together because there is only one path for the electrons to follow. Much like small groups of people walking the same direction and then merging onto the same street, the electrons form larger and larger groups (voltages/current). Parallel circuits, there are multiple paths and electrons can take any of them. They will spread out and take the path of least resistance which divides them evenly. That means you maintain a steady

9 voltage/current all along the circuit. This also tends to mean that they back one another up and can last longer. 5. The correct answer is C. The circuit in the picture is a parallel circuit. Electrons have more than one path to follow so if one bridge goes out, they can all complete the circuit through the other routes. Those bulbs would stay lit. 6. The correct answer is C. The circuit is a combination circuit. Bulb A is in parallel to bulbs B & C so the electrons can still complete the circuit by traveling through B & C. Bulbs B & C are in series to each other. If one of them went out the other would also go out (A would stay lit since it is in parallel to those 2). For #7, 8 & 9 the students would use Voltage (V) = Current (I) times resistance (R). Volts = amps times ohms (Ω). Plug in the number sin the correct location and then one step equation solve for the answer. 7. The correct answer is D. V = 6*3 = The correct answer is B. 9 = 12* R To solve divide 9 by 12 which is The correct answer is A. 120 = I* 8 To solve, divide 120 by 8 which is You calculate velocity in much the same way you calculate speed (distance divided by time). The only difference is you must add the direction. A half hour is 0.5 hours. 5/0.5 = 10 and to get to the western side of a mountain you must go west. So the answer is B. 11. To calculate acceleration you take final velocity, subtract initial (starting) velocity and then divide that

10 answer by the amount of time the change took. In this case you would do 23 8 = 15 then divide 15 by 3 which gives you 5. The correct answer is D. 12. Same as # = divided by 12 = 3. The correct answer is B. 13. Simple machines do not reduce the amount of work required. They reduce the amount of effort by increasing the distance. Work in physics means effort (Newtons) times distance (meters). 500N*10m = 5000J in the same way that 50N* 100m = 5000J A Newton meter is a Joule (J). The correct answer is C. 14. Mechanical advantage of a lever is effort/resistance in this case we re using the distances for effort and resistance. So, 24/4 = 6. The correct answer is B. 15. This one is a little trickier because it doesn t give you the distances it only gives you the length of the lever arm and where the fulcrum is located. You have to figure out the distances first. The fulcrum is placed 0.5m from the resistance so that is actually 0.5m. The distance for the effort is the total length of the arm minus the length from the fulcrum to the resistance. That means = 3.5. Now we can use our effort/resistance = mechanical advantage formula. 3.5/0.5 = 7. The correct answer is C. 16. The mechanical advantage of a ramp is found by dividing the length of the ramp by the height the object is raised. In this case 15/2.5 = 6. The correct answer is B. 17. You work this problem a bit backwards. You re given the mechanical advantage and the height and they ask you to find the length of the ramp. MA = ramp length/height. So 8 = X/1.5. So use one step equation

11 problem solving that becomes 8*1.5 =X. Multiply and you get 12. The correct answer is D. 18. For pulleys, you first check to see the direction the force is being applied pulled down or pulled up. Count the number of lines. If the force is being pulled down you do not count that line. If the force is being pulled up, the line is counted in the total. Looking at the picture you see the force (where the little letter f is) is next to an arrow pointing down. This line will not count. Count the rest across the middle. You see there are 4 lines there. The MA = Mechanical advantage for wheel and axles is equal to the measurement for the wheel divided by the measurement for the axle. As long as the two measurements are the same - diameter to diameter or radius to radius. In this case, MA = 5/1 = 5. The correct answer is C. 20. Work = force times distance. 500N is the force and 6 meters is the distance. Work = 500*6 = The correct answer is B.