Question

Q2) Calculate if the Truck can carry 5 tone freight with 50 km/h speed or not, using given information below? Truck dead weight 13 tones, truck travelling at 8% uphill slope, Air resistance coefficient=0,02 kg.sn-'m, Rolling resistance coefficient = 0,04 kg/kg, Truck wide 2,5 m Truck height 1.8 m, Engine efficiency coefficient 0.90, Truck power-380 HP.

Answer 1

Ans 2) We know,

Resistance force on truck = Air resistance + Rolling resistance + Grade resistance

=>
F Тек
= $F_{air}$ + $F_{rl}$ +
F 16

Also,

$F_{air}$ = 0.5 Cd $\rho$ A $V^2$

where, Cd = Air resistnace coefficient = 0.02

  $\rho$ = air density = 1.225 kg/m3

A = Area of truck = width x height = 2.5 x 1.8 = 4.5 $m^2$

V = Truck Speed = 50 km/hr or 13.89 m/s

=>  $F_{air}$ = 0.5 x 0.02 x 1.225 x 4.5 x 13.89 x 13.89

=> $F_{air}$ = 10.63 N

Also,

  $F_{rl}$ = Cr x W

where, W = truck weight = mg = (13000 + 5000) x 9.81 = 176580 N

Cr = Coefficient of rolling resistance = 0.04

=> $F_{rl}$ = 0.04 x 176580 = 7063.2 N

Also,

= G x W

F 16

=> = 0.08 x 176580 = 14126.4 N

F 16

Hence, total resistance force = 10.63 + 7063.2 + 14126.4 = 21200.23 N

=> Power required = Resistance force x Speed / Efficiency   

=> Power required = 21200.23 x 13.89 / 0.90

=> Power required = 327190 W or 438.60 HP

Since,available power (380 HP) is less than required power (438.6 HP) , the truck cannot carry 5 tone fright