A simple yet annoying problem

[needguidance]

Homework Statement

An 80kg man stands on an elevator what force is exerted on the elevator if it is rising with a

constant velocity of 4.0 m/s. (take account of grvitational acceleration g=9.8m/s^2)

Homework Equations

F=ma



3)attempt to solve

the time and distance is not given so I could not find the aceleration at all if it were it woul be merely simple addition of acceleration multiplied by the mass

F=m(g+a) what i want to know is that how can u calculate it with just the velocity?

 

[Doc Al]

If the velocity is constant, what's the acceleration?

 

[needguidance]

If the velocity is constant, what's the acceleration?

then the acceleration is constant aswell... but what's the value of the acceleration

 

[Doc Al]

then the acceleration is constant aswell... but what's the value of the acceleration

I want you to tell me the value of the acceleration. Just think about the definition of acceleration.

Hint: It's trivial, once you realize it.

 

[needguidance]

-___- it would be the same as when it is stationary? 9.8m/s^s...but why? if its correct

 

[Doc Al]

-___- it would be the same as when it is stationary? 9.8m/s^s...but why? if its correct

Careful. When moving at constant velocity you'll have the same acceleration as when stationary. But that's not 9.8 m/s^2!

9.8 m/s^2 is the acceleration something has when it's falling. Not when it's just sitting there.

 

[Cornraker]

then the acceleration is constant aswell... but what's the value of the acceleration

Is the velocity is constant, then there is no acceleration. Correct?