What is the time and velocity of a falling helicopter wheel?

[Elviklemon]

i got an assignment for physics and my class hasn't done a lot of vertical motion yet, it sounds like a pretty traight forward question but I am 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 I am struggling to deal with, is the initial velocity 14.7m/s?

 

[tiny-tim]

Welcome to PF!

Hi Elviklemon! Welcome to PF!

… is the initial velocity 14.7m/s?

That's right!

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

 

[Elviklemon]

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

i can't find an equation that will find the time?

 

[tiny-tim]

Hi Elviklemon!

(try using the X² icon just above the Reply box )

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

i can't find an equation that will find the time?

Learn by heart all the standard https://www.physicsforums.com/library.php?do=view_item&itemid=204" equations …

you need one beginning s = … ​

 

[Elviklemon]

i don't know how to use the x^2 thing sorry :P ,

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

 

[tiny-tim]

would the S = a negative number?

if a is negative, then s = -49

 

[Elviklemon]

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

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