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A ramp in an administrative office

Problem

Slips and falls cause a multitude of injuries that require many millions of dollars in medical treatment every year. According to one international index, the approximated cost of workplace slips, trips, and falls is estimated to be \$6.6 billion. In an effort to improve workplace conditions and reduce the amount of these occurrences, one company is investigating ways to reduce falls from workers when walking up a linoleum-floored ramp in the work hallways. A diagram of the ramp is given in figure 1.
Figure 1. The ramp in the administrative office.
One way to prevent these slips and falls is to use improved engineering strategies in designing steps, ramps, and other potential problem areas.
Employee volunteers at this office were provided socks that have a rubber coating on the bottom to improve traction. The coefficient of kinetic friction between the rubber bottomed socks and the linoleum-floored ramps are as follows:
Coefficient of static friction ${\text{μ}}_{s}$=0.5 Coefficient of kinetic friction ${\text{μ}}_{k}$=0.3
An employee is walking up the hospital ramp. If the employee is walking with normal walking motion, what force most directly prevents the walking individual from slipping?