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004 free fall

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  • 1. FREE FALLAccording to Galileo, from the result of his careful measurements, that all freely falling objects have thesame acceleration at the same place near the earth’s surface. This acceleration, which is called theacceleration of gravity (symbol g) has a worldwide average at sea level of 9.81 m/s2 (32.2 ft/sec2).We can apply the formulas for motion under constant acceleration to objects in free fall. It is importantto keep in mind that the direction of the acceleration of gravity g is always downward, no matterwhether we are dealing with a dropped object or with one that is initially thrown upward.Example 1:A stone is dropped from the top of a building 300m high. How long does it take the stone to reach theground? (Neglect air resistance). What is the velocity when it strikes the ground?Example 2:A stone is thrown upward with an initial speed of 16 m/s. Solve the following: (a) The maximum heightbe. (b) The time for the stone to return to the ground (c) The location of the stone after 0.8s. (d) Thelocation of the stone after 2.4s?
  • 2. Problems: 1. How fast must a ball be thrown upward to reach a height of 12m? 2. Divers in Acapulco leap from a point 36m above the sea. What is their velocity when they enter the water? [Ans. 27 m/s] 3. A stone is dropped from a cliff 490 m above its base. How long does the stone take to fall? 4. A bullet is fired vertically upward and returns to the ground in 20s. Find the height it reaches? 5. A ball is thrown vertically upward at 10 m/s. What is its velocity 1.0s later? 2.0s later?