Hello,

The displacement of a body is given by s = ut + 1/2 * a * t^2

Case 1: When body covers 200 cm in 2s

s = ut + 1/2 * a * t^2

200 = u * 2 + 1/2 * a * 2^2

u + a = 100 (Equation 1)

Case 2: When body covers 220 cm in next 4s, therefore in total it will cover (200+220 = 420 cm) in (2+4 = 6 sec)

s = ut + 1/2 * a * t^2

420 = u*6 + 1/2 * a * 6^2

u + 3a = 70 (Equation 2)

Solving Equation 1 and Equation 2, we get:

u = 115 cm/s and a = -15 cm/s^2

Now, v = u + at

At the end of 7 seconds, t = 7, Substituting the values in above equation, we get:

v = 115 - 15 * 7

v = 10 cm/sec (Answer)