9Under the influence of gravity alone, an object near the 3.3 Projectile MotionUnder the influence of gravity alone, an object near thesurface of the Earth will accelerate downwards at 9.80m/s2.
10ExampleA ball thrown horizontally from a 13m high building strikes the ground 5.0m from the building. With what velocity was the ball thrown?
11Solution By definition, we have y = voyt – ½ gt2 t2 = -2y/g t = 1.63sAlso, by definition we havex = voxt + ½ axt2vox = x/t= 5/1.63= 3.07m/s
12Problems to be solved3.12, 3.24, 3.41, 3.45, 3.51, 3.72B3.1 A snowball is thrown from 2m above the ground at a velocity of 10m/s directed at 30° above the horizontal. (a)How long will the snowball be in the air? (b) Where will it land?
13B3.2 Some books advice serving a tennis ball at an angle below the horizontal direction. To see if this is sound advice, suppose a ball is struck at an angle of 5° downward at a height of 2.4m with the relatively high speed of 30m/s. How high will it be when it reaches the net 12m away? (The net is 0.9m high. Neglect air resistance.)
14B3. 3 A tennis ball is served 2 B3.3 A tennis ball is served 2.5m above the ground at an angle of 5° above the horizontal direction with an initial speed of 30m/s. (a) When will it hit the ground? (b) How far will it travel?