# Induced emf

Aerospace
A 5.56m long steel beam is accidentally dropped by a construction crane from a height of 3.97m. The horizontal component of the Earth's magnetic field over the region is 28.4e-6T. Acceleration of gravity is 9.8 m/s^2.
What is the induced emf in the beam just before impact with the Earth, assuming its long dimension remains in a horizontal plane, oriented perpendicularly to the horizontal component of the Earth's magnetic field?

I sort of have an idea how to begin but the whole gravity thing is confusing me. Any help?

## Answers and Replies

paul11273
I think that gravity only plays a role since you will want to know how fast the beam is traveling through the magnetic field just before it hits the ground.

Aerospace
YUP! That's what I was thinking too. One of the equations for induced emf is E=Blv but how do I get the velocity from the gravity because i am not given a time period. It's probably something just basic...but I can't seem to grasp on it at this moment.

paul11273
Just use the kinematic equations. You are given the height it is falling from, and you know how fast it accelerates due to gravity.
Without time, use $$v_{f}^2=v_{i}^2+2a(y_{f}-y_{i})$$