Question 1
a)WD = 12 J
b) WD = Fs = mgs (lifting force = mg)
WD = 12.3 J
c) Pushing force = frictional force (a = 0)
Hence WD = Fs = 30 J
Net force = zero (F -f =0 )
WD by net force = zero
Question 2
WD by force = Fs = (ma) s = 315 J
Question 3
Net WD = area under force vs displacement graph
Given acceleration -displacement graph
find area under graph W = m(area under a-s graph) = 10 ( 200) = 2000 J
or change the x axis to force by multiplying by mass = 10 kg , then find area which will give you WD = 2000 J)
Question 4
Pushing force 70 N , friction = 50 N , multiplying by 10 m gives heat energy of 500J and 200J of KE ( 700J - 500 J)
or Net force = 20N, Net WD = 20x10=200 J , Increase in KE= 200 J (work energy thm)_
Question 5
Lift up second block to first block WD = mgh
Lift up third block WD = mg(2h)
Total WD energy in stacking up = 3 mgh
