View Full Version : Physics Question 1
abailey2011
Apr 17, 2014, 09:21 AM
A window washer pushes his brush up a vertical window at constant velocity by applying a force F as shown below. The brush weighs 12N and the coefficient of kinetic friction is 0.2. Find the magnitude of force F
ebaines
Apr 17, 2014, 11:12 AM
Hint: since the brush moves at constant velocity the sum of forces acting on it must equal zero.
CWH68
Apr 17, 2014, 01:29 PM
He pushes it up with a force of 12N, to cancel the force of gravity.
ebaines
Apr 17, 2014, 02:44 PM
I think not - the OP mentioned friction. Without seeing the diagram it's impossible to answer.
CWH68
Apr 17, 2014, 03:33 PM
True. The angle of the brush is not known. Call it a. Then,
F = 12N / (cos a - 0.2 sin a) provided tan a < 5. Otherwise, he cannot push the brush up.
P. S. a is the angle of the brush from the vertical.