Velocity –time graph for a Body of mass 10kg is shown in figure.  Work done on the Body in first two seconds of the motion is

given  m = 10kg      t = 2 sec work done by the body against retardation force =decrease in kinetic energy of the body.   u   =   50m/s  at  t   =   0 sec.   ∴    a   =    ΔvΔt   =    50−00−10  =   −5 m/s2     ∴     speed of the Body at  t  =  2 sec  is    v  =   u+at   ⇒   v  =  50+(−5) 2                            ⇒   v  =  40 m/s    ∴     using work –Energy  theory ,   W  =  Δ K.E         ⇒    W  =   12 mv2  −12mu2     ⇒    W  =   12  10×402 −12 10×502  =   −4500J