**41**. What is the cost of running seven 40 W lamps and five 80 W la mps for 12 hours of the electrical energy cost N7.00kWk?

**A.**N80.00**B.**N45.36**C.**N65.00**D.**N57.12

**Correct Option: Answer is D**

Seven 40W lamps = 7 × 40 = 280W

Five 80W lamps = 5 × 80 = 400W

Total power = 280W + 400W

= 680W

= \(\frac{680KW}{1000}\) = 0.68KW

The kilowatt hour = 0.68 KW × 12 hrs

= 8.16 KWh

Cost is N 7 per KWh

So the cost of running them = 8.16KWh × N 7/KWh

= 57.12

**42.**

**A.**5.0A**B.**3.7A**C.**4.5A**D.**4.0A

**Correct Option: Answer is B**

V = IR from ohms law

I = \(\frac{V}{R}\)

Since the resistance are in parallel

\(\frac{1}{Reff}\) = \(\frac{1}{8}\) + \(\frac{1}{12}\) + \(\frac{1}{6}\)

= \(\frac{2 + 3 + 6}{36}\) = \(\frac{11}{36}\)

Reff = \(\frac{36}{11}\) = 3.27

I = I_{1} + I_{2} + I_{3}

= \(\frac{V}{Reff}\)= \(\frac{12}{3.27}\)

= 3.669A

I = 3.7A

**43. **Calculate the time taken for a mango fruit that fall from the tree 20 m to the ground [g = 10 ms^{-2}]

**A.**10s**B.**5s**C.**4s**D.**2s

**Correct Option: Answer is D**

u = , H = 20, g = 10

From equation of motion under gravity

H = ut ± \(\frac{1}{2}\)gt^{2}, It is falling so g is +ve

H = 0 + \(\frac{1}{2}\)gt^{2}

H = \(\frac{1}{2}\)gt^{2}

2H = gt^{2}

\(\frac{2H}{g}\) = t^{2}

t = \(\frac{\sqrt{2H}}{g}\)

= \(\frac{\sqrt {2 \times 20}}{10}\)

= √4

= 2s

**44. **Which of the following is not a mechanical wave?

**A.**wave in closed pipe**B.**radio waves**C.**water waves**D.**sound waves

**Correct Option: Answer is B**

Mechanical waves require material medium for their propagation only radio waves among the options docs require a material medium

**45. **The velocity ratio of an inclined plane where angle of inclination in θ is

**A.**Sinθ**B.**Cosθ**C.**Tanθ**D.**$\frac{\mathrm{1\; /}}{\mathrm{sin}\theta}$

**Correct Option: Answer is D**

Consider an inclined plane shown below, as the effort moves along OB, the load moves is lifted up through a vertical height AB

V.R = \(\frac{\text{distance moved by effort}}{\text{distance moved by load}}\) = \(\frac{OB}{AB}\)

But Sinθ = \(\frac{opp}{hyp}\) = \(\frac{AB}{OB}\)

therefore; = \(\frac{OB}{AB}\) = \(\frac{1}{\sin \theta}\)

**46. **The volume of a fixed mass of gas is 10cm^{3} when its pressure is 400cmHg. Determine the volume of the gas when its pressure is 200cmHg.

**A.**30cm^{3}**B.**40cm^{3}**C.**50cm^{3}**D.**20cm^{3}

**Correct Option: Answer is D**

Using boyle’s law

P_{1}V_{1} = P_{2}V_{2}

V_{2} = \(\frac{P_1 V_1}{200}\) = \(\frac{400 \times 10}{200}\)

= 20cm^{3}

**47. **Which of the following representations is correct for an atom X with 28 electrons and 30 neutrons?

**A.**\(^{58}_{28}X\)**B.**\(^{30}_{28}X\)**C.**\(^{28}_{30}X\)**D.**\(^{58}_{30}X\)

**Correct Option: Answer is A**

An atom can be represented thus,

\(^{Z}_{A}X\) where Z = mass number

A = atomic number

A = number of proton = number of electrons in a free state = 28

Z = number of protons + number of neutrons = 28 + 30 = 58

\(^{58}_{28}X\)is the representation

**48. **Which of the following is true of an electrical charge?

**A.**Positive charge means deficit electrons**B.**Negative charge means excess of electrons**C.**electric current means movement of electrons**D.**All of the above

**Correct Option: Answer is D**

**49. **A man of mass 50kg ascends a flight of stains 5m high in 5 seconds. If acceleration due to gravity is 10ms−2${}^{-2}$ the power expended is

**A.**100w**B.**200w**C.**400w**D.**500w

**Correct Option: Answer is D**

Power is the time rate of doing work

i.e power = \(\frac{\text{energy}}{\text{time}}\)

Since energy = mgH

∴ power = \(\frac{mgH}{t}\)

= \(\frac{50 \times 10 \times 5}{t}\)

= 500W

**50. **Calculate the angle of minimum deviation of a 60^{o} prism of a refractive index [sin^{-1}0.75 = 49^{o}]

**A.**38.00^{o}**B.**19.47^{o}**C.**16.25^{o}**D.**49^{o}