# Energy/Work help with truth or false

1. Oct 4, 2004

### songokou77

Here it is:
A) Energy conservation law for a projectile (no friction): Potential energy decrease equals the kinetic energy increase.
B) More power is required while slowly lifting a box than while lifting it up quickly.
C) Work cannot be done in the absence of motion.
D) Energy is required to do work.
E) Work is done when the form of energy changes.
F) Without friction, the sum of the potential and kinetic energies of a body is constant.

I figure it's FTFTFF any corrections would nbe greatly appreciated

2. Oct 4, 2004

### vsage

Is it just me or are all or nearly all your answers opposite what they should be?

Edit: Here's some help for A-D

Mechanical energy = potential energy + kinetic energy.
Power = Work/Time
Work = Force * Displacement
Work's unit is the Joule

Last edited by a moderator: Oct 4, 2004
3. Oct 4, 2004

### Claude Bile

I agree with your answers to b), d) and e), but I think you need to rethink the others.

Claude.

4. Oct 4, 2004

### songokou77

Thanks, now I got TFTTTT i'm almost completly certain I am correct.

5. Oct 5, 2004

### Claude Bile

Are you sure?

Power = Energy/time;

Just by looking at the equation for power it should be obvious that to do more work per unit time (i.e. do something quickly) you need more power.

Also, with regard to part e), I can think of lots of situations where energy changes from one form to another without work being done. Find a wall, push on it, energy is being converted from chemical to heat energy, but no work is being done.

Claude.