A rock is thrown downward from an unknown height above the ground with an initia

Question

A rock is thrown downward from an unknown height above the ground with an initial speed of 10 m/s. It strikes the ground 3.0 s later. Determine the initial height of the rock above the ground. a. 44 m b. 14 m c. 74 m d. 30 m e. 60 m A stone is thrown from the top of a building with an initial velocity of 20 m/s at the angle of 40 degree above the horizontal towards northeast. The top of the building is 60 m above the ground. How much time elapses between the instant of release and the instant of impact with the ground? And how far away from the base of the building hits the ground?

Explanation / Answer

5) u = -10 m/s

t = 3s

a = -g = -9.8 m/s^2

y = ut+1/2at^2

y = -10*3-1/2*9.8*3^2

y = -30-44.1 = -74.1 m

negative sign indicates downward direction

6) h = -usin40*t+1/2gt^2

4.9t^2-20sin40*t-60 = 0

roots are t = 5.05 sec

x = ucos40*t

x = 77.37 m from the base of the building

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