In a certain class, the ratio of girls to boys was 5 to 4. If there are 80 boys in the class, how many students are there in all
2 answers:
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(a) If the particle's position (measured with some unit) at time <em>t</em> is given by <em>s(t)</em>, where
then the velocity at time <em>t</em>, <em>v(t)</em>, is given by the derivative of <em>s(t)</em>,
(b) The velocity after 3 seconds is
(c) The particle is at rest when its velocity is zero:
(d) The particle is moving in the positive direction when its position is increasing, or equivalently when its velocity is positive:
In interval notation, this happens for <em>t</em> in the interval (0, √11) or approximately (0, 3.317) s.
(e) The total distance traveled is given by the definite integral,
By definition of absolute value, we have
In part (d), we've shown that <em>v(t)</em> > 0 when -√11 < <em>t</em> < √11, so we split up the integral at <em>t</em> = √11 as
and by the fundamental theorem of calculus, since we know <em>v(t)</em> is the derivative of <em>s(t)</em>, this reduces to
