1) m=400kg, g=10ms-2 s´=20m
W=F.s = m.g.s = 400 . 10 . 20 = 80 000J = 80kJ
Vykonaná práca je 80kJ.

2.) V = 4m3, V0 = 3dm3 = 0,003m3, h = 2.4m, ρ = 2600 kg.m-3
Počet lopát : n = V: V0 = 4m3: 0,003m3 =1333 lopát
W = m.g.h.n = W = ρ.V0.g.h.n
W = 2600kg.m-3.0,003m3.10m.s-2.2,4m.1333 = 249 537,6 kg.m2.s-2 = 250.103J
W = 250 kJ
Robotník vykonal prácu 250 kJ

3) m = 600t = 600 000kg ´= 6.10ᴧ5 m = 600t = 6.10ᴧ5kg, t = 5 min = 300s, v = 54km.h-1 = 15m.s-1, f = 0,01, W = ?


Ťažná sila rušňa vykoná prácu W = 202,5 MJ.5kg, t = 5 min = 300s, v = 54km.h-1 = 15m.s-1, f = 0,01, W = ?
Fa= m.a=m.v.t-1 = 6.10ᴧ5kg . (15ms-1)300s-1 = 6.10ᴧ5kg . 0,05ms-2 = 3.10ᴧ4N
Ff= f.m.g= 0,01 . 6.10ᴧ5.10ms-2 = 6.10ᴧ4N
W= (Fa + Ft) .s = (Fa + Ft). 1/2at2= (Fa + Ft) . 1/2 . v/t . t2
W = 9 . 10ᴧ4N . 1/2. 15ms-1/300s . (300s)2 = 2,025 . 10ᴧ8 J
Ťažná sila rušňa vykoná prácu W = 202,5 MJ.