Another Block on the Wall?

Question

A block is being held against a vertical wall at a 40 degree angle with respect to the Y-axis. The weight of the block is 87.6 N. The coefficient of static friction between the block and the vertical wall is 0.540. What minimum force is required to prevent the block from sliding down the wall? What minimum force is required to start the block moving up the wall?


Where do i use the static friction coefficient? Do I use pathagorean's to find the forces at the vertical and horizontal? where does gravity come into play? any help would be great!!!

Answer 1

summing forces along x

Fsin40 - N = 0

summing forces along y

i.) minimum force preventing the block sliding down
friction force points up

Fcos40 - 87.6 + 0.54N = 0
Fcos40 - 87.6 + 0.54(Fsin40) = 0
F = 87.6/(cos40 + 0.54sin40)
F = 78.6956 N

ii. ) minimum force so that block moves up
friction force points down
F = 87.6/(cos40 - 0.54sin40)
F = 209.0996 N

static friction coefficient is used to find the frictional force preventing the block to move where the frictional force is
(0.54*Force along X) = 0.54Fsin40

u dont need to use pythagorean theorem.. just use sine and cosines..gravity causes the block to move downward, well that's it and it must be included in your equation which is 87.6 N

moreover the block weighs 87.6/9.81 = 8.92966 kg

Answer 2

When the block is in equilibrium, the sum of the forces in the upward direction equals the sum of the forces in the downward direction.

There is only one force in the upward direction, the vertical component of the applied force , F equal to Fsin40.

There are 2 forces in the downward direction: 1. the weight of the block given as 87.6N, and 2. the force of static friction, f which is equal to uN, where u is the coefficient of static friction =0.540, and N the force normal to the wall equal to Fcos40.

The sum of the 2 downward forces= the upward force

87.6+0.54Fcos40=Fsin40
87.6+0.54*0.766F=0.643F
87.6+0.41F=0.643F
87.6=0.233F
F=87.6/0.233
=376N

Any force greater than 376N will start the block moving up the wall. The minimum force required will of course be one with a magnitude very close to 376N.

Draw the block and show the forces acting on it, including its weight, the force of friction, the vertical component of the applied force F, and the horizontal component of the force F. Once you have done that you will see that it will be impractical to use Pythagorean theorem to compute the vertical and horizontal components of F. Using the trigonometric functions (sin for vertical and cos for horizontal component) of 40degrees will be the simpler approach.

Static friction as the word implies means that the body is stationary. So use the coefficient of static friction when the body is stationary, and coefficient of kinetic friction when the body is in motion.

The force of gravity is related to the weight of the body; in this problem it is 87.6N. And there's a known relationship between weight and mass: w=mg.

Answer 3

Mortar must be large, yet once you like to characteristic better capability to ascertain which you do can get some concrete anchors and ties. use the anchors to attach the binds to the modern-day blocks, then shop on with the mortar between your blocks as universal putting the binds between the blocks of your addition. through fact you're dealing with a fire i might verify your close by construction codes to ascertain if there are any added steps you ought to take.

Answer 4

Jeremy's answer looks good, no need to add anything. But i have a question, do you have the physics book with the skier on the front? I think i had this exact question a couple weeks ago. Even the answers are the same if i remember correctly. If you want to answer me, click on my profile and email me. You don't have to though, i was just wondering.