Suppose you are watching a video of a space mission and hear that a 2-pound hammer weighs 1 pound on the planet's surface. at approximately what rate would the hammer accelerate if it is dropped on the planet?

**i have the correct answer. can someone explain the math part of it? 4.9 m/s^2 i need someone to work it out.

The "weight" of anything is 

      (the object's mass)
times
      (the acceleration of gravity in the place where the object is).

Let's back up for a second, and consider why the hammer is called
"a 2-pound hammer" in the first place ? 

That's because on Earth, where the hammer has spent all of
its life so far, and where it is acted upon by Earth's gravity, it
weighs 2 pounds. 

The acceleration of gravity on Earth is 9.8 m/s².

            (weight) = (mass) x (acceleration of gravity)
so
          2 pounds = (mass) x (9.8 m/s²) .

Look at that equation.

If the left side suddenly becomes 1 pound instead of 2 pounds,
then something on the right side must also have suddenly become
1/2 of what it used to be.  It's not the mass ... mass doesn't change.
So it must have been the acceleration that changed by half ...
it became (1/2 of 9.8) = 4.9 m/s² .