[填空题]
When a ball is thrown from the top of a tall building, its heigh e8dw)z3h,)o2dm 0tni4 oycxct aboc8 :jupuchr0 ujz8c-)o(0ft - 8ttzmg ve the ground after t seconds is givenu:ug8cjro0 tc8c zm 0 ) -8tp-tzfhuj( by
s(t)=$at^2$+bt+c, where a,b,c∈R and s(t) is measured in metres. After 1 second, the ball is 84.3 m above the ground; after 2 seconds, 93.9 m; after 8 seconds, 42.3 m.
1.(1)Write down a system of three linear equations in terms of a, b and c.
(2)Hence find the values of a, b and c. a = b = c =
2.Find the height of the building. s = m
3.Find the time it takes for the ball to hit the ground. t ≈ seconds
