Tennis ball machines can throw balls with a speed of 26.8 m/s. Somebody thought

Question

Tennis ball machines can throw balls with a speed of 26.8 m/s. Somebody thought it would be a good idea to take one of these machines to the top of a building and fire balls off, to drop on the unsuspecting people below. The machine is 80.0 m above the ground, firing balls horizontally off the top of the building. a) How long does it take for one of the fired balls to hit the ground? b) What is the horizontal (x) component of the velocity when it hits the ground? c) What is the vertical (y) component of the velocity when it hits the ground? d) If someone just picked up a tennis ball and dropped it from the top of the building (without throwing it sideways), what would be the dropped ball's velocity (x and y components)? Walking to class early on a cold, wintery morning, you realize (too late) that the big hill that you need to go down is completely covered in ice. You find yourself sliding down the 15 degree slope. At the bottom (10m from where you started) there is a curb. (assume 2 sig figs) a) What is the magnitude of your acceleration as you slide down the hill? b) How long do you slide before you hit the curb? c) How fast are you going when you hit the curb?

Explanation / Answer

2. (a) as ball hites the ground,

vertical displacement, y = 0 - 80 = - 80 m

initial vertical velocity, v0y = 0

ay = - 9.8 m/s^2

Applying y = v0y t + ay t^2 / 2

- 80 = 0 - 9.8 t^2 /2

t = 4.04 sec

(b) horizontal velocity will not change.

vfx = v0x = 26.8 m/s

(c) vfy = v0y + ay t = 0 - (9.8 x 4.04)

vfy = - 39.6 m/s

(D) then vfx = 0

vfy = - 39.6 m/s

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