help with energy and momentum

Question

 

a man works at an office which produces a lot of documents.  often he has to carry heavy stacks of documents from one office to another.  on this day he, whom ways 75 kilograms, has to transport a stack of documents which weighs 10 kilograms.   he has to life them 5 meters from the floor and then carry them to an office 100 meters down the hall, where he will drop them on the floor.  he walks swiftly at a steady rate of 1 meter per second.

 

1.  what two pieces of information given in the above description will help compute the amount of work he does when he lifts the papers?

 

2.  after he has lifted the papers, he pauses to rest for a moment.  what type of energy do the papers he is holding possess?

 

3.  when he finishes carrying the papers he drops them on the floor.  what type of energy do the papers possess as they drop?

 

4.  is the energy of the stack of papers when he holds them equal to the energy of the papers dropping on the floor?  why or why not?

 

5.  if you were going to compute the momentum of him and the papers he carries them down the hall, what three pieces of information given in the description you need to use?

 

6.  based on the formula for momentum what is the momentum he and the papers he carries them down the hall?

show work.

 

7.  if you were going to compute the kinetic energy of him and the papers he carries them down the hall, what three pieces of information given in the descripton would be needed?

 

thanks and thanks

 

Answer 1

1. The mass of the papers and the height to which he lifts them.  Work = Force*distance = (mass of papers)*g*(height lifted), where g is the acceleration due to gravity = 9.8 m/sec²
2. Potential energy = m*g*h
3. The potential energy converts to kinetic energy as the papers drop
4. Energy is conserved while the papers are dropping, so the sum of potential and kinetic energies remains constant.  Initially all of the energy is potential energy.  It is all kinetic energy as it hits the floor.
5. His mass, the mass of the stack of papers, and the speed he moves.
6. (Mass of guy + Mass of papers)* (Speed he walks)
7. You need the same 3 pieces of information as problem 5 - total mass and speed.  The formula is (1/2)(mass of guy+mass of papers)*(speed)²