# 2001 JAMB Physics Past Questions & Answers - page 1

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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

Solution
(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

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

Solution
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.

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

Solution
If the bob is fully immersed in the water, then the volume of water displaced will be equal to the volume of the bob = 4/3πr3, where r is the radius of the bob.
This volume of water in the cylinder = πr2l, where r = radius of the cylinder, and l = level of water rose in the cylinder.

Therefore, π x r2 x l = 4/3 x π x 33

Then r2 = 36
r = √36
r = 6cm

4
The resultant of two forces acting on an object is maximum if the angle between them is
A 45°
B
C 90°
D 180°

Correct Option: B

Solution
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

5
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?
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

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

Solution
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 10o = 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

Solution
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.

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