Potential Energy E p = mgh

Transcription

1 Potential Energy E p = mgh if you double the mass then the PE will the value for gravity is if you double the height then the PE will Where is the Potential energy the least in the picture below? Identify two ways you could increase the potential energy P a g e

2 Kinetic Energy if you double the mass then the KE will if you double the velocity then the KE will E k = ½ mv 2 Symbols: E k means Units: m means Units: v 2 means Units: If I want to find: Then I need to know: My formula will be: My unit will be: 2 P a g e

3 Class Work 1. Theresa s 5.45 kg dog, Mr. Muggles is napping on top of 2 meter high couch. What is the potential energy of Mr. Muggles? 2. Garfield (mass = 10.5 kg) is sleeping on top of the 3 meter high couch. What is Garfield s potential energy? 3. A 200 kg pig is standing on top of a 40 meter high muddy hill. What is the pig s potential energy? 4. Tyler (mass=50-kg) is riding in a go-kart down maple avenue. a. What is Tyler s kinetic energy if he travels at 2 m/s? b. What is Tyler s kinetic energy if he travels at 4 m/s? 3 P a g e

4 Group Work 1. Alan, a hot dog vendor, is selling hot dogs on top of a hill (height = 20 m) outside of Petco Park in San Diego California. While talking to a customer, Alan s hot dog cart starts to roll down the hill. a. What is the kinetic energy of the cart as it rolls down the hill with a velocity of 3.25 m/s? b. What is the potential energy at the top of the hill? mass = 35 kg 2. True or False: If the speed of an object doubles, the kinetic energy of the object doubles. 3. If the kinetic energy of a 625-kg roller coaster car is 1.05 x 10 5 Joules: a. Determine how fast it moves. b. If the velocity of the coaster were to double what would its new Kinetic Energy be? 4. Mister Diwater, the former platform diver for the Ringling Brother's Circus, had a kinetic energy of J just prior to hitting the bucket of water. If Mister s mass is 70 kg, then what is his speed? 4 P a g e

5 HomeWork 1. In 1987, the fastest auto race in the United States was the Busch Clash in Daytona, Florida. That year, the winner s average speed was about 88 m/s. Suppose the kinetic energy of the winning car was 3,800,000 J. What was the mass of the car and its driver? 2. In 1994, Leroy Burrell of the United States set what was then a new world record for the men s 100 m run. He ran the 100 m distance with an average speed of 10.2 m/s. Assuming that he ran with constant speed, and his mass was 65-kg, what was Burrell s kinetic energy? 3. The fastest helicopter, the Westland Lynx, has a top speed of 111 m/s. If its mass was 3400 kg, what is the helicopter s kinetic energy? 4. Dan Jansen of the United States won a speed-skating competition at the 1994 Winter Olympics in Lillehammer, Norway. He did this by skating 500 m with an average speed of 14 m/s. If his kinetic energy was 6540 J, what was his mass? 5. Charlie s mass is kg, and as he ski s down the slopes his kinetic energy is 99,600 J. What speed does Charlie travel down the slopes? 6. Susie Maroney from Australia set a women s record in long-distance swimming by swimming 93,625 m in h. What was Maroney s average speed (in m/s)? If Maroney s mass was 55 kg, what was her kinetic energy? 7. Does doubling the mass OR doubling the speed have the most effect on kinetic energy? 5 P a g e

6 Conservation of Energy The idea that energy converts from one form into another without a change in the total amount is called the law of conservation of energy. The law states that energy can never be created nor destroyed just converted from one form into another. **The law of conservation of energy is one of the most important laws in physics.** (It applies to not only kinetic and potential energy, but to all forms of energy) Sample Problems mgh i + ½ mv i 2 = mgh f + ½ mv f 2 1. A 2 kg car moving with a speed of 2 m/sec starts up a hill. How high does the car roll before it stops? 2. A roller coaster has a velocity of 25 m/s at the bottom of the first hill it travels down. How high was the hill? 6 P a g e

7 Class Work 3. An arrow is fired vertically upwards (vf=0) by a bow and reaches an altitude of 134 m. Find the initial speed of the arrow on the ground level (hi=0) 4. A children s roller coaster is released from the top of a track(vi=0). If its maximum speed at ground level(hf=0) is 8 m/s, find the height it was released from. 5. A rock is dropped (vi=0) from a height of 2.7 m. How fast is it going when it hits the ground (hf=0)? 7 P a g e

8 6. Two 64 kg stick figures are performing a stunt as the diagram below shows. One stick figure stands atop a 7.0 m tower. A second stick figure stands on a light, inflexible beam balanced over large rock. The first stick figure rolls a 256 kg boulder off the edge of the tower towards the iron beam. (Warning: These are professional stunt stick figures. Don't try this at home.) What is the theoretical limit on the height to which the second stick figure can rise? Assume that stick figures obey the law of conservation of energy and the stick figures velocity at the top of his jump is zero. 7. Calculate the potential energy, kinetic energy, mechanical energy, velocity, and height of the skater at the various locations. 8 P a g e