# Vertical motion question

1. Jul 9, 2011

### Elviklemon

i got an assignment for physics and my class hasn't done alot of vertical motion yet, it sounds like a pretty traight forward question but im battling.

A helicopter is rising vertically with a velocity of 14.7m/s when its wheel drops off at a height of 49m

i) calculate the time for the wheel to reach the ground

ii) what is the velocity of the wheel on impact with the ground

im guessing when i find the time the velocity will be easy to find, the main thing im struggling to deal with, is the initial velocity 14.7m/s?

2. Jul 9, 2011

### tiny-tim

Welcome to PF!

Hi Elviklemon! Welcome to PF!
That's right!

Since it isn't pushed (it only "drops off"), its velocity will be the same as that of the helicopter.​

3. Jul 9, 2011

### Elviklemon

but in that case i have
u = 14.7m/s
s = 49m
a = -9.8m/s^-2

i cant find an equation that will find the time?

4. Jul 9, 2011

### tiny-tim

Hi Elviklemon!

(try using the X2 icon just above the Reply box )
Learn by heart all the standard https://www.physicsforums.com/library.php?do=view_item&itemid=204" equations …

you need one beginning s = …

Last edited by a moderator: Apr 26, 2017
5. Jul 9, 2011

### Elviklemon

i dont know how to use the x^2 thing sorry :P ,

would the S = a negative number? because it can only travel downwards?

6. Jul 9, 2011

### tiny-tim

if a is negative, then s = -49

7. Jul 9, 2011

### Elviklemon

Thanks heaps mate, i think i've figured her out, now i just have 4 momentum questions to go before i hand it in to my teacher in 2 days time :/

(and its great to be here at PF ;) )