JAMB Physics Past Questions & Answers - Page 460

2,296.

The velocity ratio of a machine is 5 and its efficiency is 75%. What effort would be needed to lift a load of 150N with the machine?

A.

20N

B.

30N

C.

40N

D.

50N

Correct answer is C

Efficiency = M.A/V.R
75% = M.A/V.R
75/100 = M.A/5
M.A = 75(5)/100 = 3.75

But M.A = Load/Effort
3.75 = 150/Effort
Effort = 150/3.75
Effort = 40N

2,298.

When a ship sails from salt water into fresh water, the fraction of its volume above the water surface will

A.

increase

B.

decrease

C.

remain the same

D.

increase then decrease

Correct answer is B

Fresh water is less dense than the salt water, hence when the ship sails in fresh water, it will sink more, thus the fraction of the ship above the water surface will decrease.

2,300.

A semiconductor diode is used in rectifying alternating current into direct current mainly because it

A.

allows current to flow in either direction

B.

is non-linear

C.

offers a high input resistance

D.

allows current to flow only in one direction

Correct answer is D

A rectifier of an alternating current is a device which allows the flow of current only in one direction