A ball of mass 0-1 kg is thrown against a wall. It strikes the wall normally with a velocity of 30 \[\text{m}{{\text{s}}^{\text{-1}}}\]and rebounds from there with a velocity of 20\[\text{m}{{\text{s}}^{\text{-1}}}\]. The impulse of the force exerted by the ball on the wall is

• A.  0.5 Ns           
• B.         50 Ns
• C.  5 Ns                       
• D.         1 Ns