(A)At t1 acceleration is positive therefore, displacement will be negative.
Since a=−ω2x
A->3
(B) Since acceleration is zero. therefore, displacement is zero.
B->1
(C)Since, v=∫adt
Therefore, the area of a−t curve from t=0 to t=t1 is negative therefore,
v<0
Alternatively, Just before, t1 the point where a−t curve crosses t-axis is making acceleration negative to positive and also theamax point is also after t1 therefore, particle has just crosses the mean position and it is traveling in −ve direction therefore, velocity is negative.
C->3
(D)t2 is mean position therefore, x=0 and acceleration is zero but acceleration is becoming -ve to +ve therefore, displacement is becoming +ve to -ve therefore, particle is at mean position and travelling in -ve direction therefore, velocity is -ve and maximum.
D->3,4