5. A large boulder is ejected vertically upward from a volcano with an initial s

Question

5. A large boulder is ejected vertically upward from a volcano with an initial speed of 45 m/s. Air resistance may be ignored (a) At what time after being ejected is the boulder moving at 25m/s upward? (b) At what time is it moving at 25m/s downward? (c) When is the displacement of the boulder from its initial position zero? (d) When is the velocity of the boulder zero? (e) What are the magnitude and direction of the acceleration while the boulder is () moving upward? () Moving downward? (Gi) At the highest point? ( Sketch v and y-f graphs for the motion.

Explanation / Answer

(a) 25 = 45-9.8t

t= 2.04s

(b)-25 = 45-9.8t

=7.14s

(c)-45 = 45-9.8t

=9.18s

(d) t = 9.18÷2

=4.59s

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