What does this mean? Physics Help!!!!!!!!!!!!!!!!!!!

Question

A weightlifter holds a 150 kg weight 2 m from the floor. Calculate the speed which the weight hits the floor when dropped. You may assume that no energy leaves the system, and that the gravitational field strength is 9.8/kg.

I am unsure how to calculate it and which formula to use. Is it Ek Ep or Ee. I think it's Ep but it wants the speed and is the gravitational field strength is 9.8/kg important?

Answer 1

You use both.  When the weight is being held above the floor, it has potential energy (E_p):

 

    E_p = mgh = (150 kg)(9.8 m/s²)(2 m) = 2940 joules

 

When the weight is dropped, the potential energy is converted into kinetic energy (E_k):

 

     E_k = (1/2)mv²

     2940 joules = (1/2)(150 kg)v²

 

Solve for v.  The units are m/s.