# 1998 - WAEC Physics Past Questions & Answers - page 1

1
which of the following pairs of physical quantities comprises vectors?
A
capacitance and inductance
B
force ratio and velocity ratio
C
friction and momentum
D
energy and power
CORRECT OPTION: b
2
A piece of stone attached to one end pf string is whirled round in a horizontal circle. When the string is suddenly cut, the stone will
A
move towards te centre of the circle
B
stop moving immediately
C
move along a circular path of smaller radius
D
fly off in a direction tangential to the circular path
CORRECT OPTION: d
3
The term torque means
A
the moment
B
the resultant of several forces acting on a body in equilibrum
C
two equal and oposite forces whose lines of action do not coincide
D
two coplaner forces at right angles to each other
CORRECT OPTION: a
4
A rectangular block of wood floats in water with two-thirds of its volume immersed. When placed in another liquid, it floats with half of its volume immersed. Calculate the relative density of the liquid
A
1.43
B
1.33
C
1.00
D
0.83
CORRECT OPTION: e
R.D = $$\frac{\text{volume of liquid displaced}}{\text{volume of water displaced}}$$

= $$\frac{1}{2} - \frac{2}{3} = \frac{1}{2} \times \frac{3}{2} = \frac{3}{4}$$

= 0.75
5
As the end Q of the plank is raised, the component of W, normal to plank, will
A
increase
B
decrease
C
remain the same
D
be slightly greater than W
CORRECT OPTION: b
6
If $$\theta$$ is equal to $$\alpha$$ at the time the box is just about to slide down the plank, the coefficient of static friction between the plank and box is
A
sin$$\alpha$$
B
cos$$\alpha$$
C
tan$$\alpha$$
D
sec$$\alpha$$
CORRECT OPTION: c
$$\mu = \frac{F}{R} = \frac{W sin \theta}{W cos q}$$

= tan$$\theta$$
7
I the box is pulled from P to Q, which of the following expresses the velocity ratio of the inclined plane?
A
PR/PQ
B
OR/PQ
C
OR/PR
D
PQ/PR
CORRECT OPTION: e
8

a pilot records the atmospheric pressure outside his plane as 63cm of Hg while a ground observer records a reading of 75cm of Hg with his barometer. Assuming that the density of air is constant, calculate the height of the plane above the ground. (take the relative densities of air and mecury as 0.00136 and 13.6 respectively)

A
120m
B
138m
C
274m
D
1200m
CORRECT OPTION: d

pressure change for air = pressure change for mercury

hpg = Hpg

h x 0.00136 x g = (75 - 63) x 13.6 x g

h = $$\frac{12 \times 13.6}{0.00136}$$

= 120,000cm

= 1,200m

9
An object is protected with a velocity of 100m-1 at an angle of 60o to the vertical. Calculate the time taken by the object to reach the highest point (Take g as 10ms-2
A
5.0s
B
8.7s
C
10.0s
D
17.3s
CORRECT OPTION: b
t = $$\frac{T}{2} = \frac{1}{2} = \frac{2u \sin \theta}{g} = \frac{100 \times \sin 60}{10}$$

10 sin60 = 10 x 0.8660

= 8.7
10
The earth is not a perfect sphere because its equatorial axis is longer than the polar axis. where on the earth's surface would an object have its greatest weight?
A
half way between the equator and the north pole
B
near the equator
C
half way between the equator and the south pole
D
at either pole
CORRECT OPTION: c
Pages: