# Homework Help: A simple yet annoying problem

1. Apr 22, 2010

### needguidance

1. The problem statement, all variables and given/known data
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)
2. Relevant 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?

2. Apr 22, 2010

### Staff: Mentor

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

3. Apr 22, 2010

### needguidance

then the acceleration is constant aswell.... but whats the value of the acceleration

4. Apr 22, 2010

### Staff: Mentor

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.

5. Apr 22, 2010

### needguidance

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

6. Apr 22, 2010

### Staff: Mentor

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.

7. Apr 22, 2010

### Cornraker

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