WAEC Past Questions and Answers - Page 3235

16,171.

A screw-jack has the distance between its successive threads as P and the length of its tommy bar as r. Its velocity ratio is given by the expression

A.

\(\frac{2 \pi r^2}{P}\)

B.

\(\frac{2 \pi r}{P}\)

C.

\(\frac{2 \pi}{rp}\)

D.

\(\frac{P}{2 \pi r}\)

Correct answer is B

No explanation has been provided for this answer.

16,172.

The S.I unit of power is

A.

N

B.

Pa

C.

W

D.

J

Correct answer is C

No explanation has been provided for this answer.

16,173.

A device that converts mechanical energy into electrical energy is

A.

a dynamo

B.

an electric motor

C.

an induction coil

D.

a transformer

Correct answer is A

No explanation has been provided for this answer.

16,174.

Alcohol of mass 21g and density 0.7g cm-3 is mixed with 10g of water. Determine the density of the mixture [density of water = 1.0gcm-3]

A.

0.775gcm-3

B.

0.875gcm-3

C.

0.780gcm-3

D.

0.880gcm-3

Correct answer is A

\(V_A = \frac{M}{D} = \frac{21}{0.7} = 30cm^3\)

\(V_w = \frac{M}{D} = \frac{10}{1} = 10cm^3\)

Vmixture = 30 + 10 = 40cm3

Mmixture = 21 + 10 = 31g

Dmixture = \(\frac{m}{v} = \frac{31}{40} = 0.775\)

16,175.

The period of a simple pendulum X is 5s. What is the period of a simple pendulum Y which makes 50 vibrations in the same time it takes X to make 20 vibrations?

A.

12.5s

B.

2.5s

C.

2.0s

D.

1.2s

Correct answer is C

It takes X 5s for 1 complete vibration.

⇒ It takes X (5 x 20)s for 20 vibrations.

= 100s.

It takes Y 100s for 50 vibrations.

⇒ The period of Y = \(\frac{100}{50}\)s

= 2s.