Question

QUESTION 4 (100 marks) (a) A tractor rated to deliver a total of 20 kN.m of torque (moment) at its rear wheels is to be used to drag a loaded silo, a short distance across a rough horizontal concrete surface. Given the co-efficient of friction between the steel and the concrete is 0.6, the radius of the rear wheels is 0.8 m (i) What is the maximum mass of the silo (in kg) that can be dragged with this tractor? Ignore the effect of initially getting the silo moving (20 marks) (ii) Given the power rating of the tractor at its wheels is 7.5 kW and the relationship between Power and Torque (moment) is given by P Tx w where (omega) is the rotational speed of the wheels in rad/s. What is the maximum speed (in m/s) at which the silo can be dragged with this tractor? (20 marks) (b) A 1 kg piece of aluminium at 900C is placed into 4 litres of water which is at room temperature (20°C). The density of water is 1000 kg/m3, the specific heat value of water is 4180 J/(kg.K) and the specific heat value of aluminium is 903 J/(kg.K) Assume that no heat energy is exchanged with the container or the surrounding air, no water is converted to steam What will be the final (common) temperature of the water and the aluminium once their temperatures equalise? Work in SI units. Hints: all energy is conserved, use equations to solve (30 marks)

Answer 1

0.70rau-x bichendl boreo (20x103) Co.6 (a.81)(03) T (ung) () mE 92 M-4.24%x10 POwesn = TxW-F (1)XWEKK vE(0.8)( 0.370Tad/4 20x 3 2(0.8)0.37) V 0.3 m/

Heal Jakt aluium Heal gain y Loaley A-2 Wak tra ot ate, Mal g mat at uat, Maev (05x(uxi63) = Specibic gpecitic MJ49.(T-)muGa (1-T) 4(uto) (T-20) eyG(u) (uB) 90-1 (4.) (903)(40-1) (A)C903) 06-0 WXO8 90-T 18.516 T-20 90-7-(8.516) (-20) 90+ (20X18.516) 19,516T T23.587C