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Question

https://online-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/DuPage/phys2111/summer/homework/Ch-14-SHM/friction_graph/friction-force-3.gif

A student sets up a experiment similar to one we did in lab. A 0.36 kg wood block is placed on a horizontal lab track and has a 3 kg brass mass placed on top of it. The wooden block is attached to a force probe via a light string similar to what we did in lab. The block is initially at rest and she slowly increases the tension in the string until the mass starts to move. She then pulls the block along at a constant velocity of 1.6 m/sec. The signal from the force probe produces the graph below on the computer.

a) What is the co-efficent of static friction between the wooden block and the lab track?

b)What is the co-efficent of kinetic friction between the wooden block and the lab track?

c) What would the force probe read if the student pulled the block along at a constant speed of 3.2 m/sec instead of 1.6 m/sec as she initially did ?

d) What would the force probe read if the student placed a 6 kg brass mass on the block instead of the 3 kg mass she initially used ?

Explanation / Answer

a)

F = smg

s = F/mg

s = 16 / (3.36 x 9.8) = 0.486

b)

F = kmg

k = F/mg

k = 12 / (3.36 x 9.8) = 0.3644

c)

no change, because force depends on mass and acceeration and not on velocity.

d)

F = kmg

F = 0.3644 x 6.36 x 9.8 = 22.71 N

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