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Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

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Sec. 2]_The Direction of Concavity. Po<strong>in</strong>ts of Inflection 91<br />

887*. The centres of three elastic spheres A, B\ C are situated<br />

on a s<strong>in</strong>gle straight l<strong>in</strong>e. Sphere A of mass M mov<strong>in</strong>g with ve-<br />

locity v strikes fi, which, hav<strong>in</strong>g acquired a certa<strong>in</strong> velocity,<br />

strikes C of mass m. What mass should B have so that C will<br />

have the greatest possible velocity?<br />

888. N identical electric cells can be formed <strong>in</strong>to a battery<br />

<strong>in</strong> different ways by comb<strong>in</strong><strong>in</strong>g n cells <strong>in</strong> series and then comb<strong>in</strong>-<br />

<strong>in</strong>g the result<strong>in</strong>g groups (the number of groups is<br />

allel. The current supplied by this battery is given by<br />

,<br />

~~<br />

NnS<br />

] <strong>in</strong> par-<br />

the formula<br />

where < is the electromotive force of one cell, r is its <strong>in</strong>ternal<br />

resistance, and R is its external resistance.<br />

For what<br />

current?<br />

value of n will the battery produce the greatest<br />

889. Determ<strong>in</strong>e the diameter y of a circular open<strong>in</strong>g <strong>in</strong> the<br />

body of a dam for which the discharge of water per second Q<br />

will be greatest, if Q = cy Vhtj, where h is the de<strong>pt</strong>h of the<br />

lowest po<strong>in</strong>t of the open<strong>in</strong>g (h and the empirical coefficient c are<br />

constant).<br />

890. If x lf # 2 , ..., x n are the results of measurements of equal<br />

precision of a quantity x, then its most probable value will be<br />

that for which the sum of the squares of the errors<br />

0=2 (*-*,)<br />

1=1<br />

is of least value (the pr<strong>in</strong>c<strong>ipl</strong>e of least squares).<br />

Prove that the most probable value of x is the arithmetic mean<br />

of the measurements.<br />

Sec. 2. The Direction of Concavity. Po<strong>in</strong>ts of Inflection<br />

1. The concavity of the graph of a function. We say that the graph of a<br />

differentiable function y f(x) is concave down <strong>in</strong> the <strong>in</strong>terval (a,b) [concave<br />

up <strong>in</strong> the <strong>in</strong>terval (ap 6,)] if for a

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