- #1
B3NR4Y
Gold Member
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Homework Statement
The acceleration of a particular car during braking has magnitude bt, where t is the time in seconds from the instant the car begins braking, and b = 1.5m/s3. If the car has an initial speed of 45m/s , how far does it travel before it stops?
Homework Equations
There are two equations that are relevant, I think
[itex]\vec{v_{f}}=\vec{v_{i}} + \vec{a} t[/itex]
and
[itex]\vec{d}=\vec{v_{i}} t + \frac{1}{2} \vec{a} t^{2}[/itex]
The Attempt at a Solution
I then used the first equation to find the time it took for the car to come to a complete stop, or vf = 0.
[itex] 0 = 45 (m/s) - (1.5 (m/s^{3}) t) (t) [/itex]
Simplifying and solving for t I got, [itex] t = \sqrt{30} s [/itex]
Using this in my second equation, [itex]\vec{d}=45 (m/s) \sqrt{30} s + \frac{1}{2} -(1.5 (m/s^{3})* \sqrt{30}) 30[/itex]
Using my calculator I got 123 m/s, or 120 m/s in two significant figures like the problem asked. However, this was not right apparently. Please point my vector in the right direction!