# Homework Help: Hey physics instant velocity ques

1. Sep 30, 2004

### lilman7769

If an arrow is shot upward on the moon with a velocity of 58m/s, its height in meters after t seconds is given by h=58t-0.83t^2

find the instantaneous velocity after one second....can u post ur work?? and explain this to me......thx in advance...

2. Sep 30, 2004

### Pyrrhus

Instant Velocity is

$$\vec{V} = \frac{d \vec{r}}{dt}$$

If you have this formula, then the first derivative is speed. For velocity, remember to put the j, because it's 1D motion in the y-axis.

$$h=58t-0.83t^2$$

3. Sep 30, 2004

### lilman7769

its for a calculus class and we arent allowed to use derivtives yet.......so for that forula u gave me what number would i plug in???? im kinda confused....i did a table of values with time intervals to average velocity but the whole one second i dont understand.....can u show me like an answer......im sorry ur rules are u not doing my hmk...i seriously have tried i just dont understand...

4. Sep 30, 2004

### Pyrrhus

You could graph that function, and pick really close values for time and h, to calculate the slope.

The First derivative is the slope.

Slope formula
$$m = \frac{\Delta h}{\Delta t}$$