- #1
ShizukaSm
- 85
- 0
Homework Statement
A driver sees the red light, and instead of braking the car, changes the gear to neutral. Suppose that velocity obeys this equation:
[itex]v = v_0 * e^{-bt}[/itex]
Where [itex]v_o = 20 m/s[/itex] and [itex]b = 0.150 s^{-1}[/itex]
a)Acceleration when time equals 0;(Answer:[itex]-3.0 m/s^2[/itex])
b)Displacement when [itex]t=5.0 s[/itex];(Answer:[itex]70.6m[/itex])
c)Velocity when displacement is [itex]50m[/itex].(Answer: [itex]12.5m/s[/itex])
Homework Equations
It's possible to solve using only the one supplied by the problem.
The Attempt at a Solution
I can solve letter a, but I fail at letter b and c, so I am going to post only the attempt at those:
b) Displacement is the integral of velocity in t, so, by integrating the velocity I get:
[itex]x(t)=\frac{v_o}{-b}*e^{-bt}[/itex]
and by substituting [itex]b = -0.15[/itex] and [itex]Vo = 20[/itex], I get: [itex]-62.98m[/itex]!
c) By using the displacement equation found in letter b), I equal the displacement to [itex]50m[/itex], and try to solve for t. I find [itex]t = 6.53s[/itex].
Then I substitute [itex]t=6.53s[/itex] in the velocity equation, and find that [itex]v = 7.50m/s[/itex]!