Physics Free Fall?

There is a 250-m-high cliff at Half Dome in Yosemite National Park in California. Suppose a boulder breaks loose from the top of this cliff. (a) How fast will it be going when it strikes the ground? (b)how long a time will a tourist at the bottom have to get out of the way after hearing the sound of the rock... show more There is a 250-m-high cliff at Half Dome in Yosemite National Park in California. Suppose a boulder breaks loose from the top of this cliff. (a) How fast will it be going when it strikes the ground? (b)how long a time will a tourist at the bottom have to get out of the way after hearing the sound of the rock breaking loose (neglecting reaction time and the height of the tourist, which would become negligible anyway if hit)?
Update: Please Explain
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