Below is the solution:
1) Let the acceleration is a m/s^2 and the velocity after 4 sec is v m/s
=>By v = u + at
=>v = 4a ------------(i)
For 1st phase:-
=>By s = ut + 1/2at^2
=>s1 = 0 + 1/2 x a (4)^2
=>s1 = 8a --------------(ii)
For 2nd phase:-
=>By s = vt
=>s2 = 4a x (9.1-4)
=>s2 = 20.4a -------------(iii)
=>By (ii) + (iii):-
=>s1+s2 = 8a + 20.4a
=>100 = 28.4a
=>a = 3.52 m/s^2
2)(a) By v = u -gt
=>0 = u - 9.8 x 1.5
=>u = 14.7 m/s
(b) By v^2 = u^2 - 2gh
=>0 = (14.7)^2 - 2 x 9.8 x h
=>h = 11.03 m
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