For a body projected vertically upwards, the only acceleration acting on the body is the acceleration due to gravity, acting vertically downwards (neglecting all air drag forces). That is, a = - 9 .8 m∕s2 ... (i) Using equation: v = u + at … (ii) where, u : initial velocity with which the body was projected t : time v : final velocity a! time t ⇒ V = u - gt Since u and a in eq— (ii) are constants, 'v' varies linearly with t. Or, velocity-time curve for such a body is a straight line with negative slope. Hence; option 'D' is correct