WEBVTT

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This is Giancoli Answers
with Mr. Dychko

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30 g of acceleration has
to be written in m/s squared.

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So, we'll multiply 30 g
by 9.8 m/s squared for every g.

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And so the gs cancel
and we're left with 294 m/s squared,

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and that's the acceleration
that we multiplied by mass

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to get the net force
on this person.

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And it's the net force

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because there will be
only one force acting

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on the passenger or the driver
when they're coming to the crash,

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and horizontally speaking,

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that'll be the force
exerted by the car backwards.

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So, that's 139x10^4 Newtons.

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And to calculate the distance

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that the person
will travel during the crash,

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we know
that the final velocity is zero,

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and were given the initial velocity,
95 kilometers an hour,

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and we've
calculated the acceleration.

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And we'll solve this for <i>d</i>.

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So, subtract <i>V initial squared</i>
from both sides.

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And then we get the next line
and we'll divide by <i>2a</i>, both sides.

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And we get the displacement
will be the negative of the velocity

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converted into m/s.

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This is the same as dividing by 3.6
which is what I did here

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but you can see
the units all match up,

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the hours cancel
and the kilometers cancel

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leaving us with m/s.

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And so, that's 95 kilometers an hour
times 1 hour for every 3600 seconds

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times 1,000 meters
for every kilometer.

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And square that result
and divide by 2.

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And then this acceleration is negative

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because it's going to be in
the opposite direction to the velocity

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which we've taken
to be positive inside the brackets here.

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This negative is
just from the algebra.

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And we end up with positive
1.2 meters displacement.

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So, positive
just means it'll be in the direction

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of the initial velocity, of course.

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And so the driver will go 1.2 meters
before coming to a stop.