Mj Physics Units
April 3rd, 2009 | Author: Thriller
physics help please!!anyone!!?
A train with a total mass of 3.8 × 106 kg rises
791 m while traveling a distance of 61 km at
an average speed of 11 km/h. The frictional
force is 0.8 percent of the weight.
The acceleration of gravity is 9.81 m/s2 .
Find the kinetic energy of the train.
Answer in units of MJ.
a)kinetic energy of train in units of MJ
b)Find the total change in its potential energy. Answer in units of J. (which i found to be 2.946 e10)
c)Find the energy dissipated by friction. Answer in units of J.(which i found to be 1.817312 e 10)
d)Find the power output of the train’s engines. Answer in units of MW.
i know for a fact b and c are correct but please can anyone help me with the other two.
work of friction: W = ƒ d = 0.8(3.8x10^6)(9.81)*61000 = 1819x10^9 J
power: P = Fv
Fnet = ma
The net force must overcome the component of weight along the incline and the friction force so it can accelerate up the incline.
ƒ + mg sin { arcsin(0.791/61) } = ma
0.8 mg + mg (0.791/61} = ma
a = 0.8*9.81 + 9.81(0.013) = 7.97 m/s²
F = ma = (3.8x10^6)*7.97 = 30.28x10^6 N
Power: P = Fv = 30.28x10^6 (11000/3600) = 92.54 MW
Lec 15 | 8.01 Physics I: Classical Mechanics, Fall 1999
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