Forces: Newton's Laws

Question

The kinetic coefficient of friction of a rubber tire on wet concrete is 0.70. What is the mass of a tractor that, with its brakes locked, can be dragged by a tow truck exerting a horizontal force of 1.0 x 10^4 N?

Answer 1

Assuming the tractor is dragged at constant speed (i.e. zero acceleration), equate the applied force F to the opposing force of friction f and solve for its mass.

 

F = f = μmg

 

m = F/(μg) = (1.0 x 10⁴ N) / [0.70(9.8 m/s²)] ≅ 1458 kg