2. A large boulder is ejected vertically upward from a volcano with an initial speed of 100 m/s. Air resistance may be ignored. [g = 10 m/s² ]

a. At what time after being ejected is the boulder moving at 30 m/s upward ? (5)

v_i = 100 m/s ; v_f = 30 m/s ; a = -10m/s²

b. At what time is it moving at 30 m/s downward ? (5)

Same as above except v_f = -30 m/s

c. When is the displacement of the boulder from its initial position zero ? (5)

d. When is the velocity of the boulder zero ? (5)

e. What are the magnitude and direction of the acceleration while the boulder is moving (i) upward ? (ii) downward ? (iii) at the highest point ? (2)

Acceleration is constant in magnitude (10 m/s²) and always directed downward (-y)

f. Sketch a_y , v_y and y versus t on the diagrams below (assume that y = 0 at the moment the boulder is ejected). (3)