In 6-8 find the velocity v(t) and position s(t) at time t> 0 of a material particle that moves without friction along a straight line, when its acceleration, initial position, and initial velocity are as specified. Hint: read Example 1.20 (page 7 in textbook) 6 a(t) = 2, s(0) = 4, v(0) = 0. 7 a(t) = -12 sin(2t), s(0) = 0, 8 a(t)=3(t+4)-1/2, s(0) = 1, v(0) = 6. v(0) = -1.