How Can You Calculate Mass from Force if Acceleration is Zero?

[TheOGBacon]

Homework Statement

A book exerts a force of 19.6 Newtons on the top of a desk. What is it's mass?

Homework Equations

M= Force/Acceleration

The Attempt at a Solution

I tried using the acceleration formula, but that only added more variables.

 

[phinds]

I tried using the acceleration formula, but that only added more variables.

Really? What is the acceleration due to gravity?

 

[TheOGBacon]

I meant I tried using the acceleration formula to get an expression that I could plug in for my force equation.

 

[haruspex]

meant I tried using the acceleration formula

That's the one you quoted in post #1, right?
You have a force, you want to find the mass, so all you need is an acceleration, yes?
Presumably, the force is the weight of the book. If an object has mass m, what is its weight?

 

[jbriggs444]

I meant I tried using the acceleration formula to get an expression that I could plug in for my force equation.

A somewhat different route to get there: When in doubt, always start with a free body diagram.

The acceleration of the book is zero. F=ma. So the net force on the book must be zero. What forces act on the book?