Question

Dania is dragging a 110 kg trunk across a rough floor at a constant velocity of 5.6 m/s [E] with a horizontal force of 380 N [E].

1. Calculate the coefficient of kinetic friction between the trunk and floor.
2. Sonya decides to help by pulling on the trunk with a force of 150 N [Up].  Will Sonya be helping Dania?  Explain
3. Calculate the force Dania needs to pull at now in order to keep a constant speed.
4. Another student (not as nice as Sonya) sits on the trunk.  They have a mass of 55 kg.  What force does Dania need to pull at now for a constant speed?

Answer 1

1)

$\mu=\frac F{mg}=0.35,$

2)

$\mu$ will lower, she will help,

3)

$F'=F\frac {\mu}{\mu'}=325~N,$

4)

$F''=F\frac {F'}{F'+m'g}=143~N.$