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AP Physics I U6 - WS3 - Energy & Power page 1 Unit 6 - Energy 1/26/2018 1. A pendulum with a length of L = 2.0 m is pulled back to an angle of 30" and is then released. What is the ma velocity of the bob? 2. A frictionless roller coaster tops the first hill shown to the right with a speedvo = 5 "/s. The height, h of the first hill is 30 m. a. What is its speed at point A? h/2 b. What is its speed at point B? C. What is its speed at point C? d. How high will it rise on the last hill before it rolls back? 3. A 75 g Frisbee is thrown from a height of 1. Im above the ground with a speed of 12 m/s. When it reaches a height of 2. 1 m, its speed is 10.5 m/'s. a. What is the change in the gravitational potential energy of the frisbee? b. What is the change in the kinetic energy of the frisbee? c. How much of the Frisbee's mechanical energy was dissipated by air drag? 4. A 3000 kg truck travels on a level road at a velocity of 20 m/s when it comes to the top of a 5 km long 5" downward slope. At this point, the driver discovers that his brakes have failed. . If the driver puts their truck into neutral (ur = 0), what would the truck's velocity be at the bottom of the slope? b. The driver instead puts the truck into low gear, increasing the friction in the engine so that ur = 0.08. What is the velocity of the truck at the bottom of the ramp? C. Fortunately, there is a "runaway truck ramp" at the bottom of the slope which is angled upward at 15". How long must the ramp be in order to stop the truck (Ur is still 0.08). d. If the ramp is only 50m long, what must the up be on the ramp in order to make sure that the truck stops before reaching the top of the ramp? 5. A 10 kg block slides toward a horizontal spring with a constant of 10 N/m. When the block hits the spring, its velocity is 5 m/s. What is the maximum compression of the spring if the surface is frictionless? 6. The same block from the previous problem is sliding toward the same spring, but this time, there is friction between the block and surface (Us = 0.30 and uk = 0.20). The block hits the spring with a velocity of 5 m/s. a. How far will the spring be compressed? b. What is the energy stored in the spring to this point? c. How much energy is dissipated by friction from the point when the block hits the spring until it momentarily stops at the spring's full compression? d. Where will the block eventually come to rest? (Is the spring still compressed or not?) c. What is the minimal force needed to get the block moving again? 7. An 8 kg brick rests on a spring, compressing it 10 cm. a. Draw a force diagram of all forces acting on the brick. b. What is the spring constant? K c. The brick is pushed down an additional 30 cm. What is the potential energy of the compressed spring? d. The spring (now compressed a total of 40 cm) is released. How high will the brick rise? 8. The brick from problem 7 is dropped from a height of 40 cm above the top of the uncompressed spring. 40 cm a. What is the maximum distance the spring is compressed? b. How high will the brick rise after the spring "bounces back"? c. What is the maximum velocity of the brick while in contact with the spring? K