# September 14 AP physics.

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September 14 AP physics

IN: Unbeknownst to the students, every time the school floors are waxed, Mr. Tobin likes to slide down the hallway in his socks. Mr. Tobin weighs 850 N and the coefficient of kinetic friction between his socks and the floor is What is the force of friction that opposes Mr. Tobin’s motion down the hall?

Objective: Understand the force of friction. Success criteria:
Add friction to Newton's law problems.

Homework check

A 700 kg polar bear slides across the ice with a force of friction of 25 N.
What is the coefficient of friction between fur and ice?

A 150 kg skiier slides down a 20o slope
A 150 kg skiier slides down a 20o slope. The coefficient of kinetic friction between skiis and snow is .1. What is the normal force? What is the force down the hill? What is the net force down the hill? What is his acceleration down the hill?

A 25 kg boy slides along a slip-n-slide
A 25 kg boy slides along a slip-n-slide. He slows down with an acceleration of .5 m/s2. What is µk between the slide and the boy?

A group of people pull a 200,000 kg plane with a force of 40,000 N to keep it moving at a constant velocity. What is the kinetic force of friction? What is the coefficient of kinetic friction of the tires on the tarmack?

Out: A 20 N block is being pushed across a horizontal table by an 18 N force. If the coefficient of kinetic friction between the block and the table is 0.4, find the acceleration of the block. a) 0.5 m/s2 b) 1 m/s2 c) 5 m/s2 d) 7.5 m/s2 e) 9 m/s2