1. You look up and see a rock 120 m above the ground falling through the sky. Yo

Question

1. You look up and see a rock 120 m above the ground falling through the sky. You determine its speed to be 17 m/s. Three seconds later you determine that the rock is moving at 22.1 m/s.

a. Was the rock dropped or thrown? If it was dropped, from what height was it dropped? If it was thrown, what was the velocity it was thrown at? Explain your answer thoroughly.

b. What statement(s), if any, can you make about where you are?

2. You are standing at the top of a cliff of height 125 m. Your friend is at the base of the cliff. You each have a baseball. At time zero, you drop your ball.

a. What is the maximum speed your friend can throw her ball upward and have it hit the ground before your ball does?

b. How will your baseball’s speed compare to your friend’s right before it hits the ground for this specific case?

Explanation / Answer

since the rock speed increases after three seconds the rock is moving down ward so rock was dropped

from the kinematic equation

v^2 - u^2 = 2as

the distance convered by the rock above 120 m is

s = v^2- u^2/ 2a = ( 17 m/s)^2 - 0^2/ 2 ( 9.8) = 14.74 m

so from the height where the rock was dropped is

H = 120 m+ 14.74 m = 134.74 m

you are on the ground

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