Junior Physics 2021-2022 Unit 2: Kinematics 2.10 HW: Free Fall Motion Name: _____________________________________ Period: ______ Table: ______ Date: _________ The equations of kinematics for uniform acceleration also apply to the special case of an object that is accelerating near the earth’s surface. The gravitational pull of the earth on any object will cause it to accelerate towards the centre of the earth at a rate of 9.80 m/s2, assuming air resistance is negligible. Thus, for any equations involving a body in free fall (something that is dropped or thrown) we can use the same problem-solving skills we already have. There are a few unique features to solving freefall problems. ● acceleration is always constant at g = 9.8 m/s2 downward, or -9.8 m/s2 (the negative is very important) ● at the top of its flight, an object has vi = 0. (since it must stop before starting to come down again) ● keeping your sign conventions for direction is very important...all velocity directed down must be negative, and all velocity directed up must be positive. Equations and constant you need to use: g = 9.8 m/s2, vf = - gt and Δx = h = - ½ gt2 1. An astronaut on the Moon drops a tool from rest. After 1.3 s the tool has a velocity of 2.1 m/s [down]. Determine the acceleration due to gravity on the Moon. 2. An apple drops from a tree and undergoes free fall motion toward the ground. a. Sketch the shape of the velocity-time graph of the apple’s motion, assuming that downward is positive. b. What is the slope of the line on your graph and what does the slope represent? 3. In the Wizard of Oz, Dorothy awakens in Munchkinland where her house has just fallen a distance of 3000. m. With what speed did it hit the Wicked Witch of East when it landed? 4. Perhaps sometime in the near future, NASA will develop a program to land humans on Mars. If you were on Mars and discovered that when you dropped a hammer it took .68 s to fall .90 m to the ground, what would you calculate for the gravitational acceleration of Mars? 5. You are walking in Paris alongside the Eiffel Tower and suddenly a croissant smacks you on the head and knocks you to the ground. From your handy dandy tourist guidebook, you find that the height of the Eiffel Tower is 300.5 m. Calculate how many seconds the croissant dropped before it tagged you on the head. Ignore the air resistance. 6. A textbook is dropped from the roof of a building here on earth. It takes 8.0s to hit the ground. a. What distance did the textbook fall? b. At the instant before the textbook hits the ground, what is its velocity? c. How long would it take for the textbook to fall 45.0 m? 7. A tourist drops a rock from rest from a guard rail overlooking a valley. a. What is the velocity of the rock at 4.0 s? b. What is the displacement of the rock at 4.0 s? 8. A man is standing on the edge of a 20.0 m high cliff. He throws a rock vertically with an initial velocity of 10.0 m/s. a. Sketch the free fall motion and mark the height of each position. b. How high does the rock go? (Remember that at its max height v = 0 m/s) c. How long does it take to reach its max height?
