Force given velocity and mass?

In summary, the conversation discusses determining the apparent weight of a passenger in an elevator at different time intervals. The correct acceleration must be determined and all forces acting on the person must be considered before using Newton's laws. The concept of gravity and its constant effect on weight is important to consider when calculating apparent weight.
  • #1
alexas
52
0

Homework Statement



The figure shows the velocity graph of a 75kg passenger in an elevator.

What is the passenger's apparent weight at t= 1 s ?
What is the passenger's apparent weight at t= 5 s ?
What is the passenger's apparent weight at t= 9 s ?

Homework Equations



F = ma


The Attempt at a Solution



I was thinking since the acceleartion at 1s is 4m/s
The answer for 1s is 300N?

5s, since acceleration is 0, it would be: 0?



Anyways, my answers ended up not being accepted. So i know I am definitely doing something wrong. Any ideas?
 
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  • #2
We don't see your velocity-teme graph; you first have to determine the correct acceleration, not velocity, at each time interval. Then when you apply Newton's laws, you must first look at all forces acting on the person before using F_net = ma. The 'apparent weight' is the Normal force acting on the person.
 
  • #3
Heres the picture
 

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  • #4
I was basing the acceleration on the rate of change that was occurring.
 
  • #5
alexas said:
I was basing the acceleration on the rate of change that was occurring.

It's accelerating because of the increase in speed, this is true, but what about gravity?
 
  • #6
First let me just say, when you are standing in an elevator, before it begins to move, do you weigh zero?

Think about that for a second, I'm not sure why you would have submitted that but I admit I've had my share of braindead moments myself so I can't be pointing any fingers. Hehehe.

For apparent weight I usually add the acceleration that the system is undergoing TO gravity itself which you must remember (and apparently did not =p ) never goes away.

So yea, think about it.
 

1. What is the formula for calculating force given velocity and mass?

The formula for calculating force is F = m x a, where F is force, m is mass, and a is acceleration. To find acceleration, you can also use the formula a = Δv/Δt, where Δv is change in velocity and Δt is change in time.

2. How does mass affect the force given a certain velocity?

The greater the mass, the greater the force needed to achieve the same velocity. This is because mass is a measure of an object's resistance to acceleration. A heavier object requires more force to move at the same speed as a lighter object.

3. Can force and velocity be used interchangeably in the formula?

No, force and velocity are two different quantities that cannot be used interchangeably. Force is a vector quantity that measures the strength of a push or pull, while velocity is a vector quantity that measures the speed and direction of an object's motion.

4. How does the direction of force affect an object's motion?

The direction of force is important in determining the direction of an object's motion. If the force is applied in the same direction as the object's velocity, it will increase the object's speed. If the force is applied in the opposite direction, it will decrease the object's speed. If the force is applied perpendicularly to the object's velocity, it will cause the object to change direction.

5. What units are used to measure force?

The SI unit for force is Newton (N). Other commonly used units include pound (lb) and kilogram-force (kgf). In the formula F = m x a, the mass should be in kilograms (kg) and the acceleration in meters per second squared (m/s²) for the result to be in Newtons (N).

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