# 2018 - WAEC Physics Past Questions and Answers - page 1

The S.I unit for sound energy is

Hz

cd

dB

J

The general definition of elastic modulus is

**correct option:**a

Elastic modulus is the ratio of pressure (stress) applied to a body to the resistance (strain) produced by the body.

= \(\frac{stress}{strain}\)

The diagram above illustrates a simple barometer. Which distance measures the atmospheric pressure?

PQ

QR

RS

QS

**correct option:**b

The height of the mercury column in a simple barometer is equivalent to the atmospheric pressure.

The property of a body to remain at rest or to continue in uniform motion in a straight line is called

**correct option:**b

Inertia is the resistance of the object to any change in its motion, including a change in direction. An object will stay still or keep moving at the same speed and in a straight line, unless it is acted upon by an external unbalanced force.

During a training session, two footballers pass a ball repeatedly between each other. The 'to and fro' motion of the ball is not simple harmonic because the

I. Acceleration of the ball is not directed towards a fixed point

II. Restoring force is not directed towards the centre

III. Acceleration of the ball is not directly proportional to the displacement from a fixed point

Which of the statements above are correct?

I and III only

I and II only

II and III only

I, II and III

**correct option:**a

In Simple Harmonic Motion, the body in motion must have acceleration in a direction opposite to the displacement and the acceleration is directly proportional to displacement and is directed towards its mean position.

A dam is able to hold a large quantity of water because its wall is

thickest at the top

thickest at the middle

thickest at the bottom

of the same thickness throughout

**correct option:**c

The pressure of the water is greater deeper towards the bottom hence, the dam needs to be thicker at the bottom so it is strong enough to withstand this larger pressure.

A body of mass **m **moving around a circle of radius **r **with a uniform speed **v **experiences a centripetal force **F. **The work done by the centripetal force on it is

Fv

zero

Fmr

\(\frac{Fr}{m}\)

**correct option:**b

Work done by centripetal force in a uniform circular motion is 0 Joules.

A block is acted upon by TWO horizontal forces as illustrated in the diagram above. The block accelerates at 1.5\(ms^{-2}\). Calculate the mass of the block.

6kg

9kg

10kg

15kg

**correct option:**a

Total force exerted on the block = (10 - 1) = 9N

Force = mass x acceleration

9 = m x 1.5

m = 9/1.5 = 6kg

Which of the following quantities are dimensionally independent?

I. Dielectric constant II. Momentum III. Efficiency IV. Refractive index

I and II

II, III and IV

I, II, III and IV

I, III and IV

**correct option:**d

Efficiency, Dielectric constant and Refractive index are dimensionless quantities.

A body is projected with an initial velocity **u** at angle \(\theta\) to the horizontal. If \(R_{max}\) is the maximum range of the projectile, what does the relation \(\frac{u^{2}}{R_{max}}\) represent?

The vertical distance covered

Acceleration due to gravity

The horizontal distance covered

The acceleration of the body

**correct option:**b

\(R_{max} = \frac{u^{2}}{g}\)

\(g = \frac{u^{2}}{R_{max}}\)