Taking only the cart plus equipment as the system, of mass 19.0 kg accelerating at 1.5 m/s^2 against 24.0 N of opposing force, what force does the lecturer exert on the cart?

1. With the cart and equipment as the system, the push of the lecturer becomes an external force. 2. The net external force is that push minus the opposing force of 24.0 N. 3. Newton's second law gives the net force as the mass times the acceleration. 4. Substitute the values: (19.0 kg)(1.5 m/s^2) = 29 N. 5. Rearranged, the push equals the net force plus the opposing force. 6. Substitute again: 29 N + 24.0 N = 53 N. 7. This is far less than the 150 N she pushed on the floor, since part of that force accelerates her own body. _Source: OpenStax College Physics (CC BY 4.0), Ch 4 "Dynamics: Force and Newton's Laws of Motion", section 4.4 Newton's Third Law of Motion: Symmetry in Forces_