Bill and Joan working with force and acceleration

Question

Bill and Joan tug on a frictonless wagon having mass 20kg.  If Joan is pulling with 120N of force, and the crate has an acceleration of 1.5m/s^{2 in the direction of Bill, how hard is Bill pulling?}

Answer 1

∑F = ma   F_J + F_B = ma  (J for Joan and B for Bill.)

120 + F_B = 20 * 1.5        120 + F_B = 30     F_B = -90N   

Bill is pulling -90N.

 

Good luck.