# Homework Help: Irodov Problem

1. Jan 22, 2008

### danilo_rj

A body of mass m is thrown at an angle alpha to the horizontal with the initial velocity v0. Find the mean power developed by gravity over the whole time of motion of the body, and the instantaneous power of gravity as a function of time.

I didn't understand why delta r is orthogonal to mg. Where delta r is the net displacement of the body during time of flight.

Last edited: Jan 22, 2008
2. Jan 22, 2008

### Staff: Mentor

Where does the body begin and end its motion? What's the direction of that displacement?

3. Jan 22, 2008

### danilo_rj

what is said in the problem is only this, there is no picture.

4. Jan 22, 2008

### Staff: Mentor

You are given all the information needed to answer my question.

5. Jan 22, 2008

### danilo_rj

Ok. So I have to suppose that the beggining and the ending of the motion is at a same plane.

6. Jan 22, 2008

### Staff: Mentor

Exactly.

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