A ball travels 200cm in the first 2sec and 220cmin the next 5sec. Find the velocity at 7s
s = 1/2 at^2
v = at
assuming it started from rest, and had constant acceleration in each period,
s1 = 1/2 * a1 * 2^2 = 200
a1 = 100 cm/s^2
v1 = a1*t = 100*2 = 200cm/s
s2 = 200*5 + 1/2 * a2 * 5^2 = 220
a2 = -62.4 cm/s^2
v2 = v1 + a2 * 5 = 200 - 5*62.4 = -112 cm/s
Seems a bit odd. Maybe my assumptions are not correct.