Originally posted by Uncertain:
lol.... just as my nick implies i also dun know i am right
a not but i will give some of my reasoning:
To Eagle:
I think i found some mistake in your working, please pardon me if i
identiy them wrongly i also sort of lost touch liao.
1) Your working: If we assume [b]constant speed
intially,
initial upward force = 8.82x 10^4 N
if we assume constant speed, then acceleration = 0, then force = 0
right?
2) I think u forget to resolve the forces. The force exerted by the
two cars opposes the force exerted by the engine. Hence, we need to
find the Resultant force.
3) I think the "Assume the original speed was 2.8 m/s" serves a
bait to confuse the problem solver.
Ok, now i will write my working:
Total masses of the 2 cars: 1.2x10^4 x 2 = 2.4 x 10^4 kg
Force exerted by the cars along the slope = 2.4 x 10^4 x 9.81 x
sin22
= 88197.376 N
Resultant Upward Force = 0.9 x 10^5 - 88197.376 = 1802.624N
Retardation Force by engine due to throttle back = 3.3 N/s
i.e. Time needed for the force to reach 0 = 1802.624 / 3.3 = 546
s
OK... this is the time need for the train to come to a halt from an
inital velocity of 2.8m/s. After which, the train will begin to
slip back down again if the engine continue to throttle
back.[/b]
I thought of that, but 0.9 x 10^5 is the MAX force of the
engine, not the initial driving force.
Which is why I wonder if any details are left out
