4.10

4.10
· 4.10 understand that work done is equal to energy transferred

PFY p.112 & Collins p. 91

1. a) The work done (measured in "joules") is equal to the "force" (in newtons) multiplied by the "distance" moved (in metres)
b) 1 joule is the work done when a force of one "newton" moves though a distance of one "metre" (in the direction of "force")
d) Work done = "energy" transferred

2. A man lifts a parcel weighting 5 newtons from the ground on to a shelf 2 metres high. How much work does he do on the parcel?
Wd = F x d
Wd = 5 x 2
Wd = 10 J

4. A girl weighing 500 N climbs 40 m vertically when walking up the stairs in an office block. How much work does she do against gravity? What are the energy transfers here?
Wd = F x d
Wd = 500 x 40
Wd = 20,000 J

food = chemical potential energy ---> walking up = kinetic energy ---> at the top = gravitational potential energy

Q1) 50,000 J of work are done as a crane lifts a load of 400 kg. How far did the crane lift the load? (gravitational field strength, g, is 10 N/kg.)
Wd = F x d
d = Wd/F
d = 50,000/400x10
d = 12.5 m