Newton's Second Law: Solving for Acceleration and Velocity | Homework Help

AI Thread Summary
The discussion revolves around solving a physics homework problem related to Newton's Second Law, specifically focusing on acceleration and velocity. The user is attempting to derive equations for motion under braking forces and air resistance, starting with the equation F=ma. For part a, they express the relationship between mass, acceleration, and forces but seek clarity on the initial velocity and its implications for part b. They confirm that the initial speed is 15 m/s and acknowledge that this speed decreases over time. The conversation emphasizes the need to integrate the derived equation to find the velocity function v(t), rather than determining the constant k, which is assumed to be provided.
lauraosborn
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Homework Statement


http://postimage.org/image/810vdcuvf/


Homework Equations



F=ma

The Attempt at a Solution



for part a) i put mdv/dt = -F(brake) - kv

but is lost for what to put in for part b), help?
 
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What is v at t = 0?
 
Doc Al said:
What is v at t = 0?

for part b) am i right if i say that

-the speed is 15 when t=0
-the speed is decreasing
 
lauraosborn said:
for part b) am i right if i say that

-the speed is 15 when t=0
-the speed is decreasing
The first is what I would call the initial condition.
 
c) 1200 dv/dt = -(3600 + kv)
1/(3600+kv) dv = -1/1200 dt

so do i integrate the above equation to find k?
 
You're not finding k (I assume that k is given in your model of air resistance), but v(t).
 
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