Resistive FORCE of 80 N will be offered by the ground., in the direction opposite to the MOTION of cannon after firing the BALL.Explanation:Given,MASS of cannon ball, m = 2 kgMass of cannon, M = half tonne = 500 kg Final velocity of cannon ball, v = 100 m/sLet, final velocity of cannon = VDistance covered by cannon after firing the ball, s = 0.5 m To find,Resistive force offered by the ground to the motion of the cannon, F =?Solution,Initially both Cannon and ball would be at rest, therefore Initial velocity of Cannon ball = Initial velocity of cannon = u = 0Using LAW of conservation of momentum → m u + M u = m v + M V→ m (0) + M (0) = ( 2 ) ( 100 ) + ( 500 ) V→ 0 = 200 + 500 V→ V = -200/500→ V = -0.4 m/s Now, Let acceleration of cannon after firing the ball be a then, After firing the ball cannon will have U = V = -0.4 m/s as initial velocity and it will cover a distance of s = 0.5 m to come to rest hence, final velocity will be V' = 0Using third equation of motion for cannon→ 2 a s = V'² - U²→ 2 a ( 0.5 ) = ( 0 )² - ( -0.4 )²→ a = -0.16  m/s²Now, Using newton's second law of motion for cannon→ F = M a → F = ( 500 ) · ( -0.16 )→ F = -80 NTherefore, A resistive force of 80 Newtons will be offered by the Ground, in the direction opposite to the motion of Cannon after firing the ball.