Question

3. The figure below show two blocks X and Y of masses m and 2m respectively, placed on a smooth horizontal surface. m 2m XY If the blocks are accelerated by a force F, express the force exerted on block X by block Y in terms of F.

Answer 1

Considering xy to be a whole system on which an external force F is being applied assuming the net acceleration of system = a_net = a (m/s^2) this would also imply to the fact that acl particles in the system would also be morning with the same acceleration. Net mass of system = m_0 = m_z + m_y = m + 2m = 3m so, applying second equation of motion to the system F_net = m_0 alpha_net rightdoublearrow a_net = F_net/m_0 a_net = a = F/3m (1) 0 Now, drawing the free body diagram of x as we can see that, F_x_y & F_y_z or contact forces and they form an action reaction pair, which says by Newton's third law of motion that, to every action there is an equal & opposite reaction. F_xy = -F_yz or F_yx = -F_xy so, applying Newtons second law of motion to block x (F_net)_x = m_x.a_net = m_x.a