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Not sure if the question is sophisticated enough to be posted here, but here goes...
I am trying to work out the velocity-time relationship for a vehicle under certain conditions. The 'certain conditions' are:
1. deceleration due to aerodynamic drag and rolling friction
2. acceleration due to an engine less drag and friction
now, i will address the deceleration first. I tried to do model this in two ways:
a) Equilibrium of forces giving: -D - f = ma (where D=drag, f=friction). putting in the known values, i get the value of acceleration in terms of velocity as:
a = -0.00075v2-0.2943
i know that a=dv/dt, so re-arranging, i get: dt=dv/a as a=f(v)
Integrating this, i got:
v = 19.8 x tan (((t1-t)/67.3) - tan-1(v/19.8))
now, QUESTION: does this formulation make sense? and second, would the angle be in radians or degrees?
i put in values both in degrees and radians, but found the deceleration to be quite fast with radians and very slow with degrees. By fast and slow, i mean not in sync with practice. For example:
with radians, the vehicle goes from 10 m/s to 5m/s in 15s with a fairly constant gradient. Does it make sense?
b) with the basic conservation of energy equation, starting from:
KE1 - (Pf + PD)xt = KE2
Putting the values in, i got this relationship b/w time-velocity:
t = 666.7 x (100 - v2)/(v x (v2+392.4))
the deceleration (v-t) curve i got was more moderate, with a markedly decreasing gradient
QUESTION: How do these two methods compare?
What am i doing wrong?
What else should i be doing?
I am trying to work out the velocity-time relationship for a vehicle under certain conditions. The 'certain conditions' are:
1. deceleration due to aerodynamic drag and rolling friction
2. acceleration due to an engine less drag and friction
now, i will address the deceleration first. I tried to do model this in two ways:
a) Equilibrium of forces giving: -D - f = ma (where D=drag, f=friction). putting in the known values, i get the value of acceleration in terms of velocity as:
a = -0.00075v2-0.2943
i know that a=dv/dt, so re-arranging, i get: dt=dv/a as a=f(v)
Integrating this, i got:
v = 19.8 x tan (((t1-t)/67.3) - tan-1(v/19.8))
now, QUESTION: does this formulation make sense? and second, would the angle be in radians or degrees?
i put in values both in degrees and radians, but found the deceleration to be quite fast with radians and very slow with degrees. By fast and slow, i mean not in sync with practice. For example:
with radians, the vehicle goes from 10 m/s to 5m/s in 15s with a fairly constant gradient. Does it make sense?
b) with the basic conservation of energy equation, starting from:
KE1 - (Pf + PD)xt = KE2
Putting the values in, i got this relationship b/w time-velocity:
t = 666.7 x (100 - v2)/(v x (v2+392.4))
the deceleration (v-t) curve i got was more moderate, with a markedly decreasing gradient
QUESTION: How do these two methods compare?
What am i doing wrong?
What else should i be doing?