An object of mass 2 kg is kept in a lift which moves upwards. Velocity of the lift varies with time as shown in the graph. Work done (in J) by normal contact force of the lift on the block, during the time t = 0 to t = 4 s is _______.

For time interval, t = 0 to 2 sec
N = mg + ma = 2(10+1) = 22 N
For time interval, t = 2 sec to 3 sec
N = mg = 20 N
For time interval, t = 3 sec to 4 sec
$\begin{array}{l}\mathrm{N}=\mathrm{mg}-\mathrm{ma}=20-2\times 2=16 \mathrm{N}\\ {\mathrm{W}}_1=22\times \frac{1}{2}\times \left(1\right)\times (2{)}^2=44 \mathrm{J}\\ {\mathrm{W}}_2=20\times (2\times 1)=40 \mathrm{J}\\ {\mathrm{W}}_3=16\times \frac{1}{2}\times \left(2\right)\times (1{)}^2=16 \mathrm{J}\\ {\mathrm{W}}_{\text{total }}=44+40+16\Rightarrow 100 \mathrm{J}\end{array}$