WAEC Physics Past Questions & Answers - Page 8

36.

A 100 kg device is pulled up a plane inclined at 30° to the horizontal with a force of 1000 N. If the coefficient of friction between the device and the surface is 0.25, determine the total force opposing the motion.
[ g = 10 ms-2]

A.

283.5N

B.

975.0N

C.

216.5N

D.

716.5N

Correct answer is D

The forces opposing the motion of the device are "mgsin θ" and "μN" where N is the normal reaction
From the diagram, on resolving to components, N = mgcos θ
Total opposing force = mgsin θ + μmgcos θ = mg(sin θ + μcos θ)
= 100 × 10 × (sin 30° + 0.25 × cos 30°)
= 1000 × (0.5 + 0.2165)
= 1000 × 0.7165
= 716.5 N

37.

The most appropriate value of fuse for a kettle rated 220 V, 1.06 kW is

A.

3A

B.

6A

C.

5A

D.

4A

Correct answer is C

V = 220V, P = 1.60KW = 1060W, I = ?

P = IV

I = \(\frac{P}{V} = \frac{1060}{220}\)

 ≈ 5A.

38.

An atom in an excited state is one whose

A.

electrons are in the conduction band.

B.

potential energy is minimum.

C.

potential energy is maximum.

D.

electrons have moved to a higher energy level.

Correct answer is D

An atom in an excited state is one whose electrons have moved to a higher energy level.

In an atom, electrons are typically found in specific energy levels or orbitals. When an electron absorbs energy, it can move from a lower energy level to a higher energy level, which is referred to as an excited state. In this higher energy state, the electron is farther from the nucleus and has more potential energy. When the electron returns to its lower energy level, it emits the excess energy as electromagnetic radiation, often in the form of visible light. This is what gives rise to the characteristic spectral lines observed in spectroscopy.

39.

A planet has mass, M, and radius R, If the universal gravitational constant is G, what is the expression for the escape velocity of an object on the planet?

A.

\(\frac{\sqrt{GR}}{2}\)

B.

\(\frac{\sqrt{2GM}}{R}\)

C.

\(\frac{\sqrt{2G}}{R}\)

D.

\(\frac{\sqrt{GM}}{R}\)

Correct answer is B

The expression for the escape velocity \(v_e\) of an object from a planet of mass M and radius R using the universal gravitational constant G is:


\(v_e = \frac{\sqrt{2GM}}{R}\)
 

40.

Which of these is a derived unit?

A.

Kilogram

B.

Metre

C.

Newton

D.

Second

Correct answer is C

Examples of Fundamental Quantities ; Mass, kilogram, kg ; Electric Current, ampere, A ; Temperature, kelvin, K ; Amount of Substance, mole, Mol.