A large boulder is ejected vertically upward from a volcano with an initial speed of 40.0 m/s. Ignore air resistance. (a) At what time after being ejected is the boulder moving at 20.0 m/s upward? (b) At what time is it moving at 20.0 m/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 (i) moving upward? (ii) Moving downward? (iii) At the highest point? (f) Sketch ay-t, vy-t, and y-t graphs for the motion.

Solution 48 E Step 1 : Considering the data given Initial velocity of the boulder v = 40i0 m/s We need to find the time by the boulder to move upward Final velocity v = f0.0 m/s The acceleration acting upon the boulder is given by gravitational force Hence we have a = g = 9.8 m/s 2 Since the boulder is moving against gravitational force Thus we get g = 9.8 m/s 2