WAEC Further Mathematics Past Questions & Answers - Page 75

371.

Two forces (2i - 5j)N and (-3i + 4j)N act on a body of mass 5kg. Find in \(ms^{-2}\), the magnitude of the acceleration of the body.

A.

\(\frac{\sqrt{2}}{5}\)

B.

\(5\sqrt{2}\)

C.

\(2\sqrt{5}\)

D.

\(\frac{5\sqrt{2}}{2}\)

Correct answer is A

\(F = F_{1} + F_{2}\)

\((2i - 5j) + (-3i + 4j) = (-i - j)\)

\(F = ma \implies (-1, -1) = 5a\)

\(a = (-\frac{1}{5}, -\frac{1}{5})\)

\(|a| = \sqrt{(\frac{-1}{5})^2 + (\frac{-1}{5})^2} = \sqrt{2}{25}\)

\(|a| = \frac{\sqrt{2}}{5} ms^{-2}\)

372.

Yomi was asked to label four seats S, R, P, Q. What is the probability he labelled them in alphabetical order?

A.

\(\frac{1}{24}\)

B.

\(\frac{1}{6}\)

C.

\(\frac{2}{13}\)

D.

\(\frac{1}{4}\)

Correct answer is A

The number of arrangements for the 4 letters = \(^{4}P_{4} = \frac{4!}{(4 - 4)!}\)

\(4! = 24\)

Alphabetical order is just 1 of the arrangements for the letters 

= \(\frac{1}{24}\)

373.

Find the direction cosines of the vector \(4i - 3j\).

A.

\(\frac{9}{10}, \frac{27}{10}\)

B.

\(\frac{17}{27}, -\frac{17}{27}\)

C.

\(\frac{4}{5}, -\frac{3}{5}\)

D.

\(\frac{4}{7}, \frac{-3}{7}\)

Correct answer is C

Given \(V = xi +yj\), the direction cosines are \(\frac{x}{|V|}, \frac{y}{|V|}\).

\(|4i - 3j| = \sqrt{4^{2} + (-3)^{2}} = \sqrt{25} = 5\)

Direction cosines = \(\frac{4}{5}, \frac{-3}{5}\).

374.

If \(\overrightarrow{OA} = 3i + 4j\) and \(\overrightarrow{OB} = 5i - 6j \) where O is the origin and M is the midpoint of AB, find OM

A.

-2i - 10j

B.

-2i + 2j

C.

4i - j

D.

4i + j

Correct answer is C

\(\overrightarrow{OA} = (3, 4)\)

\(\overrightarrow{OB} = (5, -6)\)

\(\overrightarrow{OM} = (\frac{3 + 5}{2}, \frac{4 + (-6)}{2})\)

= \((4, -1) = 4i - j\)

375.

Find the least value of n for which \(^{3n}C_{2} > 0, n \in R\)

A.

\(\frac{1}{3}\)

B.

\(\frac{1}{6}\)

C.

\(\frac{2}{3}\)

D.

1

Correct answer is C

\(^{3n}C_{2} > 0 \implies \frac{3n!}{(3n - 2)! 2!} > 0\)

\(\frac{3n(3n - 1)(3n - 2)!}{(3n - 2)! 2} > 0\)

\(\frac{3n(3n - 1)}{2} > 0\)

\(3n(3n - 1) > 0 \implies n > 0; n > \frac{1}{3}\)

The least number in the option that satisfies \(n > 0; n > \frac{1}{3} = \frac{2}{3}\)