Problem: A rock thrown with speed 10.5 m/s and launch angle 30.0° (above the horizontal) travels a horizontal distance of = 18.0 m before hitting the ground. Use the value = 9.810 for the free-fall acceleration. (a) Find the height (yi) from which the rock was launched. Express your answer in meters to three significant figures. (b) A second rock is thrown straight upward with a speed 5.250 m/s. If this rock takes 1.979 seconds to fall to the ground, from what height was it released? Express your answer in meters to three significant figures.

FREE Expert Solution

Time taken for both the horizontal motion (which is the same as the time for the vertical motion) is expressed as:

t=Δxvx

The height along the vertical direction from which the rock was launched is given as:

yf-yi=v0t+12at2

a)

Get time from the first equation, as

t = 18.0/(10.5)cos(30.0°) = 1.979 s

a = - g = -9.810 m/s2 

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Problem Details
A rock thrown with speed 10.5 m/s and launch angle 30.0° (above the horizontal) travels a horizontal distance of = 18.0 m before hitting the ground. Use the value = 9.810 for the free-fall acceleration. 
(a) Find the height (yi) from which the rock was launched. Express your answer in meters to three significant figures. 
(b) A second rock is thrown straight upward with a speed 5.250 m/s. If this rock takes 1.979 seconds to fall to the ground, from what height was it released? Express your answer in meters to three significant figures.

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