# 2001 - JAMB Physics Past Questions and Answers - page 1

1

The height at which the atmosphere ceases to exist is about 80km. If the atmospheric pressure on the ground level is 760mmHg, the pressure at a height of 20km above the ground level is

A

380mmHg

B

570mmHg

C

190mmHg

D

480mmHg

**correct option:**b

(p - 760)/(0 - 760) = (h - 0)/(80 - 0)

∴ (p - 760)/-760 = (20 - 0)/80

80(p-760) = -760(20-0)

∴80p - 60800 = -15200

80p = 60800 - 15200

80p = 45600

∴ p = 45600/80

p = 570mmHg

Users' Answers & Comments∴ (p - 760)/-760 = (20 - 0)/80

80(p-760) = -760(20-0)

∴80p - 60800 = -15200

80p = 60800 - 15200

80p = 45600

∴ p = 45600/80

p = 570mmHg

2

A stone of mass 1kg is dropped from a height of 10m above the ground and falls freely under gravity. Its kinetic energy 5m above the ground is then equal to

A

its kinetic energy on the ground

B

twice its initial potential energy

C

its initial potential energy

D

half its initial potential energy

**correct option:**d

At the height of 10m, its total energy is potential, given by P.E. = mgh = 1 x 10 x 10 = 100J.

But as the stone descends, its potential energy decreases, while its kinetic energy increases.

Half way during the fall, (h = 5m), its P.E. = 50J, and consequently, its K.E. should be 50J, such that from the principle of conservation of energy, the total energy of the stone at any instant should be conserved.

Users' Answers & CommentsBut as the stone descends, its potential energy decreases, while its kinetic energy increases.

Half way during the fall, (h = 5m), its P.E. = 50J, and consequently, its K.E. should be 50J, such that from the principle of conservation of energy, the total energy of the stone at any instant should be conserved.

3

If a spherical metal bob of radius 3cm is fully immersed in a cylinder containing water and the water level rises by 1cm, what is the radius of the cylinder?

A

12cm

B

1cm

C

3cm

D

6cm

**correct option:**d

If the bob is fully immersed in the water, then the volume of water displaced will be equal to the volume of the bob = 4/3πr

This volume of water in the cylinder = πr

Therefore, π x r

Then r

r = √36

r = 6cm

Users' Answers & Comments^{3}, where r is the radius of the bob.This volume of water in the cylinder = πr

^{2}l, where r = radius of the cylinder, and l = level of water rose in the cylinder.Therefore, π x r

^{2}x l = 4/3 x π x 3^{3}Then r

^{2}= 36r = √36

r = 6cm

4

The resultant of two forces acting on an object is maximum if the angle between them is

A

45°

B

0°

C

90°

D

180°

**correct option:**b

The resultant of two forces acting on an object is maximum when the angle between them is zero, during which the tow forces are parallel and pointing in the same direction

Users' Answers & Comments5

I. The earth is not spherical but elliptical in shape

II. Variation in latitude and longitude

III. Rotation of the earth on its axis

IV. Variation in the density of the earth

On which combination of the above does the weight of an object vary on the earth's surface?

II. Variation in latitude and longitude

III. Rotation of the earth on its axis

IV. Variation in the density of the earth

On which combination of the above does the weight of an object vary on the earth's surface?

A

I, II, III and IV

B

II, III and IV only

C

I, II and III only

D

I and II only

**correct option:**d

6

The efficiency of a machine is always less than 100% because the

A

work output is always greater than the work input

B

load lifted is always greater than the effort applied

C

effort applied is always greater than the load lifted

D

velocity ratio is always greater than the mechanical advantage

**correct option:**d

7

Which of the following consists entirely of vector quantities?

A

Velocity, magnetic fulx and reaction

B

Tension, magnetic flux and mass

C

Displacement, impulse and power

D

Work, pressure and moment

**correct option:**a

8

Ice cubes are added to a glass of warm water. The glass and water are cooled by

A

conduction only

B

convection only

C

conduction and convection

D

convection and radiation

**correct option:**c

9

A ray of light strikes a plane mirror at an angle of incidence of 35°. If the mirror is rotated through 10°, through what angle is the reflected ray rotated?

A

70°

B

45°

C

25°

D

20°

**correct option:**d

When ever a ray of light is incident on a plane mirror at an angle of incidence l, if the mirror is then rotated through an angle θ, then the reflected ray is rotated through an angle twice θ

So if θ = 35°, then the reflected ray is rotated through 2 x 10

Users' Answers & CommentsSo if θ = 35°, then the reflected ray is rotated through 2 x 10

^{o}= 20°10

The terrestrial telescope has one extra lens more than the astronomical telescope. The extra lens is for

A

improving the sharpness

B

creating an inverted image

C

magnification of the image

D

erection of the image

**correct option:**d

The extra lens in the terrestrial telescope mounted at the middle between the objective lens and the eye piece is to re-invert the image so that it is upright.

Users' Answers & Comments