Answer #2
In the laboratory, you are given a metal block, about the size of a brick. You are also given a 2.0-m-long
wooden plank with a pulley attached to one end. Your goal is to determine experimentally the coefficient
of kinetic friction, μ (^) k , between the metal block and the wooden plank.
(a) From the list below, select the additional equipment you will need to do your experiment by
checking the line to the left of each item. Indicate if you intend to use more than one of an item.
(b) Draw a labeled diagram showing how the plank, the metal block, and the additional equipment you
selected will be used to measure μ (^) k.
(c) Briefly outline the procedure you will use, being explicit about what measurements you need to
make and how these measurements will be used to determine μ (^) k.
Determine the mass, m , of the block with the balance. The weight of the block is mg . Attach a string to
the block and pass the string over the pulley. Hang masses from the other end of the string, changing the
amount of mass until the block can move across the plank at constant speed. Use the motion detector to
verify that the speed of the block is as close to constant as possible.
The block is in equilibrium. So, the weight of the hanging masses is equal to the friction force on the
block; the normal force on the block is equal to its weight. The coefficient of kinetic friction is thus equal
to the weight of the hanging masses divided by the block’s weight.