Here u = 50 m/s , what t = 0

$$\alpha $$  =  $${{\Delta v} \over {\Delta t}}$$  =  $${{50 - 0} \over {0 - 10}}$$  =  $$-$$5 m/s²

Speed of the body at t = 2 s

v   =   u + at

=  50 + ($$-$$ 5) $$ \times $$ 2

=  40 m/s

From work energy theorem,

$$\Delta $$w  =  $${1 \over 2}m{v^2} - {1 \over 2}m{u^2}$$

=  $${1 \over 2}$$ m(v² $$-$$u²)

= $${1 \over 2}$$ $$ \times $$ 10 $$ \times $$ (40² $$-$$ 50²)

=  5 $$ \times $$ ($$-$$10)(90)

=  $$-$$ 4500 J