JAMB Physics Past Questions & Answers - Page 98

486.

In an experiment in which a molten substance is allowed to cool, the cooling curve above was obtained. The temperature 60oC is known as the

vaporization point

cooling temperature

boiling point

melting point

View answer & explanation

Correct answer is D

No explanation has been provided for this answer.

487.

A battery of emf 24V is connected to three resistor P, Q and R as illustrated in the diagram. Determine the voltage across the resistor Q

10v

14v

24v

View answer & explanation

Correct answer is B

E - V₁ + V₂

24V = 14V + VQP

VQP = 4 + 14V

VQP =10V

488.

A quantity of hot water at 100^oC is added to 400g of water at 10^oC until the temperature of the mixture is 60^oC.
Calculate the mass of the hot water added. [Specific heat capacity of water =4200JKg^-1 K^-1]

200g

320g

400g

500g

View answer & explanation

Correct answer is D

Heat lost by hot water = Heat gained by cold water

M x 4200 x (100 - 60 = 0.4 x 4200 x (60 - 10)

4200m x 40 = 0.4 x 4200 x 50

40m = 0.4 x 50

m = \(\frac{0.4 \times 50}{40}\) = 0.5kg

= 500g

489.

The diagram above illustrates a block ans tackle pulley system in which an effort E supports a load of 100.0N. If the efficiency of the machine is 75%, calculate the value of E

22.2N

38.0N

67.0N

75.0N

View answer & explanation

Correct answer is A

Given; VR = 6, e = 75%, MA = ?

e = \(\frac{\text{MA}}{\text{VR}} \times \frac{100}{1}\)

MA =\(\frac{75 \times 6}{10}\)

MA = \(\frac{9}{2}\)

MA = \(\frac{L}{E} = \frac{100}{E}\)

\(\frac{9}{2} = \frac{100}{E}\)

9E = 100

E = \(\frac{200}{9}\)

= 22.2N