Final answer:
The force of friction on the bookcase is 662 N.
Step-by-step explanation:
The force of friction on the bookcase can be found using the equation:
friction force = coefficient of static friction * normal force
The normal force is equal to the weight of the bookcase, which can be found using the equation:
weight = mass * gravity
Substituting the given values:
weight = 75 kg * 9.8 m/s^2
The coefficient of static friction is 0.9, so the force of friction can be calculated as:
friction force = 0.9 * weight
Substituting the weight value:
friction force = 0.9 * (75 kg * 9.8 m/s^2)
Solving this equation gives an answer of 662 N.