Answer:
The combined velocity of the girl and the platform after the jump is 1.14 m/s.
Explanation:
From the law of conservation of momentum:
m1u1 = (m1 + m2)v
m1 is mass of the girl = 39 kg
m2 is mass of the hanging platform = 125 kg
u1 is initial speed of the girl = 4.8 m/s
v is combined velocity of the girl and the platform after the jump
v = m1u1/(m1+m2) = 39×4.8/(39+125) = 187.2/164 = 1.14 m/s
By using Ohm's law, we can calculate the resistance of the wire. Ohm's law states that:
where V is the potential difference across the conductor, I is the current and R the resistance. Rearranging the equation, we get
Now we can use the following equation to calculate the length of the wire:
(1)
where
is the resistivity of the material
L is the length of the conductor
A is its cross-sectional area
In this problem, we have a wire of copper, with resistivity
. The radius of the wire is half the diameter:
And the cross-sectional area is
So now we can rearrange eq.(1) to calculate the length of the wire:
Motion must be defined relative to something.
Here's an obvious, everyday example:
-- You're in a passenger jet, going to visit grandma on the
coast for the holidays.
-- You're sitting still in your seat, listening to some 'mp3's,
reading a book, and dozing off.
-- At the same time, people on the ground see you flying over
at almost 500 miles per hour.
Are you moving at 500 mph, or are you not moving at all ?
The answer is 'Yes. Both.'. It just depends on who's measuring your speed.
There's no such thing as your "real" speed. Motion is always
relative to something. Different reference = different speed.