# Homework Help: Induced emf

1. Mar 30, 2004

### 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?

2. Mar 30, 2004

### 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.

3. Mar 31, 2004

### 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.

4. Mar 31, 2004

### 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 $$v_{f}^2=v_{i}^2+2a(y_{f}-y_{i})$$