How Do You Calculate the Acceleration of an iPad on a Frictional Surface?

[JamesG]

Homework Statement

At 1.0KG Apple Ipad Tablet computer is pushed horizontally with a force of 40.0N. The Coefficient of kinetic friction, between the tablet and the table equals .40
Calculate the acceleration of the ipad

Homework Equations

Ff = (.4)(1)(-9.8)
Fnet = 40N+.4-3.92

The Attempt at a Solution

Fnet = 3.52
Fnet = mass x A
Fnet = 1.0 x 3.52
A = 3.52 m/s^2

I've tried and tried, I have NO idea what I'm doing wrong. Everyone failed this test in our class, so he is letting us make test corrections. I've literally spent all night trying to figure this out, and this is my last resort. If you could just show me how to set up an equation, or give me advice. I'm not necessarily asking you do the problem for me, because I would never learn. I just need serious help.

 

[Dickfore]

why are you multiplying the friction coefficient twice?

 

[JamesG]

Where?

 

[JamesG]

I thought I only multiplied .40 once

What did I do wrong?

 

[gneill]

Detail your calculation of Fnet.

 

[JamesG]

What do you mean? Fnet = 40N + .40 (coefficient of friction) - 3.92

I got 3.92 by Ff = (.4)(1)(-9.80) = -3.92

so thenFf = 40 + .4 - 3.92 = 36.48

Fnet = 40-36.48 = 3.92

 

[gneill]

What do you mean?


Fnet = 40N + .40 (coefficient of friction) - 3.92

I got 3.92 by Ff = (.4)(1)(-9.80) = -3.92

Why are you adding the coefficient of friction to Fnet? It's a unit-less coefficient. Forces have the units of Newtons. Your Ff calculation looks fine (assuming that you understand what the (1) represents).

so then


Ff = 40 + .4 - 3.92 = 36.48

Fnet = 40-36.48 = 3.92

Why are you recalculating Ff? and Fnet?

Fnet is the sum of the forces acting. Fnet = F(applied) + F(friction).