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

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To calculate mass from force when acceleration is zero, it's essential to recognize that the force exerted by the book (19.6 Newtons) is its weight, which is the product of mass and gravitational acceleration. The equation M = Force/Acceleration cannot be directly applied since acceleration is zero, indicating that the net force acting on the book is balanced. The discussion emphasizes the importance of understanding that the weight of the book equals the gravitational force acting on it. A free body diagram can help visualize the forces at play, confirming that the gravitational force is countered by the normal force from the desk. Ultimately, the mass can be derived by recognizing the relationship between weight and gravitational acceleration.
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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.
 
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TheOGBacon said:
I tried using the acceleration formula, but that only added more variables.
Really? What is the acceleration due to gravity?
 
I meant I tried using the acceleration formula to get an expression that I could plug in for my force equation.
 
TheOGBacon said:
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?
 
TheOGBacon said:
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?
 

Thread 'Magnitude of buoyant force in fluids of different densities'

The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?
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