Forces Energy
Physics- energy/forces help?
I’m really stuck on this question. We have just started looking at energy and forces. The question is :
1) A man pulls a heavy box across a horizontal floor. He finds that he has to exert a horizontal force of 60N to move the box.
a: If he moves the box 3.4m how much work has he done (answer 60N * 3.4m = 204J)
b: If the mass of the box is 65kg, what is its weight? (answer 65g * 10N/kg = 650N)
I am stuck on parts c and d:
c: How much work does the man do against the weight of the box?
d: Explain your answer to part c.
What does this mean? It doesn’t haveanything to do with Kinetic energy or Gravitational potential energy because kinetic requires veolcity and gravitational requires a vertical height. So is it that I times the 204J by the weight of 650N? I have no idea!
Please explain it to me rather than just giving me the answer. All help appreciated.
you are correct in parts a and b
for parts c and d, remember that in order for work to be done, a force must be exerted through a distance in the direction of the force
if he exerts a horizontal force, then he does no work against the weight of the box since the weight vector is straight down
he does work aginst friction, but with a horizontal pushing force, does not do work against weight
Real World: Work, Force, Energy and Motion
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