# Can't Figure out what I am doing wrong F=MA (easy problem)

• lanzjohn
In summary, a 1020kg elevator is designed to have a maximum acceleration of 0.062 g. To calculate the maximum force the motor should exert, we use the equation F=MA and take into account the force of gravity as well. Therefore, the required force for the motor is the sum of the force due to acceleration and the force due to gravity, which is F=mg+ma.
lanzjohn

## Homework Statement

An elevator (mass 1020kg) is to be designed so that the maximum acceleration is 0.062 g. What is the maximum force the motor should exert on the supporting cable?

F=MA

## The Attempt at a Solution

(.062)(9.8 m/s^2) = .6076 m/s^2

F = (1020)(.6076)

F = 619.752 N

Why is that wrong?! Unless g means something else I don't understand what's up?

The elevator accelerates upward. What force(s) act on it? Is it only the force of the motor?

ehild

You've missed out the force on the elevator due to gravity.
F=mg+ma
gives the required force 'F' that the motor must exert to accelerate upwards at acceleration 'a'

Well there is the force of gravity. But isn't that already incorporated into the acceleration of the motor?

I guess there is the Force of tension as well...

Ohh I gotcha. I guess I assumed the tension of the rope canceled out the force of gravity... So it just left the acceleration or Force rather due to the motor. We are just starting to learn dynamics so I am a little shaky on some concepts... Got to love summer classes- they move so damn fast.

Sorry, I realize I just gave an answer without helping lanzjohn to figure it out on his own.
But I think he just forgot, since I did that a lot when I was first doing these types of questions.

## 1. What is F=MA and how do you solve it?

F=MA is the formula for Newton's Second Law of Motion, which states that the force (F) acting on an object is equal to its mass (M) multiplied by its acceleration (A). To solve for any of the variables, you must have values for the other two variables. You can then rearrange the equation to solve for the desired variable.

## 2. What is an easy problem involving F=MA?

An example of an easy problem involving F=MA would be to find the acceleration of a 5 kg object when a force of 10 N is applied to it.

## 3. What are some common mistakes when solving F=MA problems?

Some common mistakes when solving F=MA problems include not converting units correctly, forgetting to include the units in the final answer, and using incorrect values for the variables. It is important to double check your work and make sure all units are consistent.

## 4. Can F=MA be used for objects with varying mass?

Yes, F=MA can be used for objects with varying mass as long as the mass and acceleration are both taken into account. In these cases, it may be helpful to use the formula F=mg to find the force due to gravity, and then use F=MA to find the net force acting on the object.

## 5. What are some real-life applications of F=MA?

F=MA has many real-life applications, including calculating the force needed to launch a rocket into space, determining the stopping distance of a car, and understanding the motion of objects in sports such as baseball or football. It is also used in engineering and design, such as in building bridges and structures.

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