WAEC Past Questions and Answers - Page 1189

5,941.

An object is thrown vertically upwards from the top of a cliff with a velocity of \(25ms^{-1}\). Find the time, in seconds, when it is 20 metres above the cliff. \([g = 10ms^{-2}]\).

A.

0 and 1

B.

0 and 4

C.

0 and 5

D.

1 and 4

Correct answer is D

\(s = ut + \frac{at^{2}}{2}\)

This movement is against gravity, so it is negative.

\(s = ut - \frac{gt^{2}}{2}\)

\(s = 20m, u = 25ms^{-1}\)

\(20 = 25t - \frac{10t^{2}}{2} \implies 20 = 25t - 5t^{2}\)

\(5t^{2} - 25t + 20 = 0 \)

\(5t^{2} - 5t - 20t + 20 = 0 \implies 5t(t - 1) - 20(t - 1) = 0\)

\(5t - 20 = \text{0 or t - 1 = 0}\)

\(t = \text{1 or 4}\)

5,942.

Given that \(P = \begin{pmatrix} y - 2 & y - 1 \\ y - 4 & y + 2 \end{pmatrix}\) and |P| = -23, find the value of y.

A.

-4

B.

-3

C.

-1

D.

2

Correct answer is B

\(P = begin{pmatrix} y - 2 & y - 1 \\ y - 4 & y + 2 \end{pmatrix}\)

\(|P| = (y - 2)(y + 2) - (y - 1)(y - 4) = (y^{2} - 4) - (y^{2} - 5y + 4) = -23\)

\(5y - 8 = -23 \implies 5y = -23 + 8 = -15\)

\(y = \frac{-15}{5} = -3\)

5,943.

Given that \(\frac{\mathrm d y}{\mathrm d x} = \sqrt{x}\), find y.

A.

\(2x^{\frac{3}{2}} + c\)

B.

\(\frac{2}{3}x^{\frac{3}{2}} + c\)

C.

\(\frac{3}{2}x^{\frac{3}{2}} + c\)

D.

\(\frac{2}{3}x^{2} + c\)

Correct answer is B

\(\frac{\mathrm d y}{\mathrm d x} = \sqrt{x} = x^{\frac{1}{2}}\)

\(y = \int x^{\frac{1}{2}} \mathrm {d} x\)

= \(\frac{x^{\frac{1}{2} + 1}}{\frac{1}{2} + 1} + c = \frac{x^{\frac{3}{2}}}{\frac{3}{2}} + c \)

= \(\frac{2}{3}x^{\frac{3}{2}} + c\)

5,944.

Find the range of values of x for which \(x^{2} + 4x + 5\) is less than \(3x^{2} - x + 2\)

A.

\(x > \frac{-1}{2}, x > 3\)

B.

\(x < \frac{-1}{2}, x > 3\)

C.

\(\frac{-1}{2} \leq x \leq 3\)

D.

\(\frac{-1}{2} < x < 3\)

Correct answer is B

No explanation has been provided for this answer.

5,945.

The fourth term of an exponential sequence is 192 and its ninth term is 6. Find the common ratio of the sequence.

A.

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

B.

\(\frac{1}{2}\)

C.

\(2\)

D.

\(3\)

Correct answer is B

\(T_{n} = ar^{n - 1}\)

\(T_{4} = ar^{4 - 1} = ar^{3} = 192\)

\(T_{9} = ar^{9 - 1} = ar^{8} = 6\)

Dividing \(T_{9}\) by \(T_{4}\), 

\(r^{8 - 3} = \frac{6}{192}\)

\(r^{5} = \frac{1}{32} = (\frac{1}{2})^{5}\)

\(r = \frac{1}{2}\)