WAEC Physics Past Questions & Answers - Page 269

1,341.

Hot water at a temperature of t is added to twice that amount of water at a temperature of 30°C. If the resulting temperature of the mixture is 50°C. Calculate t.

A.

90oC

B.

80oC

C.

50oC

D.

40oC

E.

30oC.

Correct answer is A

Final Temperature = \(\frac{m_1 T_1 + m_2 T_2}{m_1 + m_2}\)

where m\(_1\) and m\(_2\) are the weights of the water in the first and second containers.

T\(_1\) and T\(_2\) are the temperatures of the water in the first and second container.

Given Final temperature = 50°C;

Let m\(_1\) = b, then m\(_2\) = 2b.

T\(_1\) = t; T\(_2\) = 30°C

\(\therefore 50 = \frac{b(t) + 2b(30)}{b + 2b}\)

\(50 = \frac{bt + 2b(30)}{3b}\)

\(50(3b) = bt + 2b(30) \implies 150b = b(t + 60)\)

\(150 = t + 60 \implies t = 150 - 60 = 90°C\)

1,343.
1,344.
1,345.

A body weighing 10 N in air is partially immersed in water. It displaces water of mass 0.3 kg. What is the upthrust on the body? (g = 10 ms-2)

A.

13.0 N

B.

7.0 N

C.

3.3N

D.

3.0N

E.

0.3N

Correct answer is D

No explanation has been provided for this answer.