WAEC Physics Past Questions & Answers - Page 77

381.

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

382.

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.

383.

The diagram above illustrates a uniform metre rule which is balanced on a pivot by some masses. Calculate the value of M

A.

500.0g

B.

400.0g

C.

44.4g

D.

25.0g

Correct answer is D

clockwise moment = Anti-clock wise moment

= M x 40 = 100 x 10

M = \(\frac{1000}{40}\)

= 25g

384.

A car starts from rest and covers a distance of 40m in 10s. Calculate the magnitude of its acceleration

A.

0.25ms-2

B.

0.80ms-2

C.

3.20ms-2

D.

4.00ms-2

Correct answer is B

S = ut + \(\frac{1}{2} at^2\)

40 = 0 x 10 + \(\frac{1}{2}\) x a x 102

50a = 40

a = \(\frac{40}{50}\)

= 0.8ms-2