Posted by Melissa on .
A 12 kg toboggan is pulled along at a constant velocity on a horizontal surface by a horizontal force of 11 N
How much horizontal force is needed to pull the toboggan at a constant velocity if two 57 kg girls are sitting in it ?

physics 
Elena,
The projections of the equation of motion are
x: F – F(fr) = 0
y: N  m• g = 0
F = F(fr) = K• N= k• m• g.
k = F/m• g = 11/(12•9.8) = 0.093.
The projections of the equation of motion in the second case are
x: F1 – F1(fr) = 0
y: N  M• g = 0
F1 = F1(fr) = k• N1 =k• M• g = 0.093• (2•57+)•9.8 = 114.8 N