WAEC Physics Past Questions & Answers - Page 86

426.

A body of mass 11kg is suspended from a ceiling fan by an aluminum wire of length 2m and diameter 2mm. Calculate the elastic energy stored in the wire [Young's modulus of aluminum is 7.0 x 1010Nm-2, g = 10ms-2, \(\pi\) = 3.142]`

A.

1.1 x 10-1J

B.

5.5 x 10-2J

C.

1.1 x 10-4J

D.

5.5 x 10-8J

Correct answer is B

e = \(\frac{4FI}{Y \pi d^2} = \frac{4 \times 11 \times 10 \times 2}{7 \times 10^3 \times 3.14(2 \times 10^{-2})^2}\)

= 0.001m

E = \(\frac{1}{2} Fe = \frac{1}{2} \times 110 \times 0.001\)

= 5.5 x 10-2J

427.

From Newton's first law of motion,

A.

a body can only undergo translational motion

B.

once a body remains at rest no force acts on it

C.

the net force acting in uniform linear motion is zero

D.

a body's inertia is its weight

Correct answer is C

The key point of this law is that if there is no net force resulting from unbalanced forces acting on an object. If all the external forces cancel each other out, then the object will maintain a constant velocity.

428.

The maximum displacement on either side of the equilibrium position of an object in simple harmonic motion represents

A.

period

B.

amplitude

C.

wavelength

D.

frequency

Correct answer is B

No explanation has been provided for this answer.

429.

A body of mass 20g projected vertically upwards in vacuum returns to the point of projection after 1.2s. [g = 10ms-2]. Determine the potential energy of the body at the maximum height of its motion

A.

0.36J

B.

0.72J

C.

360.00J

D.

720.00J

Correct answer is A

P.E at max = K.E on projection

= \(\frac{1}{2}\)mv2 = \(\frac{1}{2} \times 0.02 \times 6^2 = 0.36J\)

430.