JAMB Physics Past Questions & Answers - Page 350

1,746.

The equation PaVbTc= constant reduces to Charles Law if

A.

a=1, b=1and c=0

B.

a=1, b=0 and c=-1

C.

a=0, b=1 and c=1

D.

a=0, b=1 and c=-1

Correct answer is D

if a=0, b=1 and c=-1 then
P0V1T-1 = V/T (Charles Law)

1,747.

What is the equivalent of 20K in Celsius scale?

A.

-253oC

B.

-293oC

C.

68oC

D.

36oC

Correct answer is A

= (20 - 273)°C

= -253°C

1,748.

The small droplets of water that form on the grass in the early hours of the morning is

A.

Fog

B.

Haul

C.

Mist

D.

Dew

Correct answer is D

No explanation has been provided for this answer.

1,749.

A wheel and an axle is used to raise a load whose weight is 800N when an effort of 250N is applied. If the radii of the wheel and axle are 800mm and 200mm respectively, the efficiency of the machine is

A.

90%

B.

80%

C.

85%

D.

87%

Correct answer is B

VR = 800/200 = 4
\(Efficiency = \frac{MA}{VR} \times \frac{100}{1}\)

\(Efficiency = \frac{L}{E} \times \frac{1}{VR} \times \frac{100}{1}\)

\(Efficiency = \frac{800}{250} \times \frac{1}{4} \times \frac{100}{1}\)

= 78.74%
= 80%

1,750.

A machine whose efficiency is 75% is used to lift a load of 1000N. Calculate the effort put in to the machine if it has a Velocity ratio of 4.

A.

343.32N

B.

233.33N

C.

333.33N

D.

334.33N

Correct answer is C

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

\(\frac{L}{E}\frac{1}{VR}\times\frac{100}{1}=75\)

\(\frac{1000}{E}\frac{1}{4}\times\frac{100}{1}=75\)

\(E = \frac{250 \times 100}{75}\)

E = 333.3N