JAMB Physics Past Questions & Answers - Page 79

391.

The density of 400cm\(^3\) of palm oil was 0.9gcm-3 before frying. If the density of the oil was 0.6gcm-3 after frying, assuming no loss of oil due to spilling, its new volume was?

A.

1360cm\(^3\)

B.

600cm\(^3\)

C.

240cm\(^3\)

D.

8000m\(^3\)

Correct answer is B

\(Density= \frac{mass}{volume}\)

⇒ \(0.9gcm^{-3} = \frac{mass}{400cm^{3}} = 360g\)

without any loss in the frying process, we have

\(0.6gcm^{-3} = \frac{360g}{v}\)

\(v = \frac{360g}{0.6gcm^{-3}} = 600cm^{3}\) 

392.

A man walks 1km due east and then 1 km due north His displacement?

A.

√2km N 45°E

B.

1km N 30°E

C.

1km N 15°E

D.

√2km N 60°E

Correct answer is A

His movements 1km due east and then 1 km due north make a Right-Angled Triangle.

Using Pythagoras' theorem;

The Resultant becomes the Hypotenuse [h]

Hyp\(^2\) = Adj\(^2\) + \Opp(^2\)

Hyp\(^2\) = 1\(^2\) + 1\(^2\)

Hyp\(^2\) = 2 → Hyp = √2

: Resultant = √2

DIRECTION TAN Ø = \(\frac{OPP}{ADJ}\) 

TAN Ø = \(\frac{1}{1}\)

Ø = TAN\(^{-1}\) [1]

Ø= 45°

Displacement is √2km N 45°E

393.

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 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

394.

The volume of a fixed mass of gas is 10cm3 when its pressure is 400cmHg. Determine the volume of the gas when its pressure is 200cmHg.

A.

30cm3

B.

40cm3

C.

50cm3

D.

20cm3

Correct answer is D

Using boyle's law

P1V1 = P2V2

V2 = \(\frac{P_1 V_1}{200}\) = \(\frac{400 \times 10}{200}\)

= 20cm3

395.

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

A.

Sinθ

B.

Cosθ

C.

Tanθ

D.

\(\frac{1}{\sin \theta}\)

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