# A block of mass 20kg is pushed against a vertical wall by force P. The coefficient of friction between the surface and the block is 0.2. If theta = 30 degrees, what is the minimum magnitude of P to hold the block still?I understand that in order for the block to sit motionless, the net forces acting on the block must be zero. I set my equation to be Net Force = 0 = Psin(theta) + Force Friction - Force Gravity.Which I rearranged as P = (Force Gravity - Force Friction)/sin(theta) or P = (mg-μ(mg))/sin(theta)Doing this gives me a value of 313.6N rather than 202.9N which I should be getting. What am I doing wrong?

Physics for Scientists and Engineers: Foundations and Connections
1st Edition
ISBN:9781133939146
Author:Katz, Debora M.
Publisher:Katz, Debora M.
Chapter5: Newton's Laws Of Motion
Section: Chapter Questions
Problem 23PQ: The x and y coordinates of a 4.00-kg particle moving in the xy plane under the influence of a net...
Question

A block of mass 20kg is pushed against a vertical wall by force P. The coefficient of friction between the surface and the block is 0.2. If theta = 30 degrees, what is the minimum magnitude of P to hold the block still?
I understand that in order for the block to sit motionless, the net forces acting on the block must be zero. I set my equation to be Net Force = 0 = Psin(theta) + Force Friction - Force Gravity.
Which I rearranged as P = (Force Gravity - Force Friction)/sin(theta) or P = (mg-μ(mg))/sin(theta)
Doing this gives me a value of 313.6N rather than 202.9N which I should be getting. What am I doing wrong?

Expert Solution

Trending now

This is a popular solution!

Step by step

Solved in 5 steps with 7 images