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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

View answer & explanation

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

View answer & explanation

Correct answer is C

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

P = IV

I = $\frac{P}{V} = \frac{1060}{220}$

≈ 5A.

38.

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.

$\frac{\sqrt{GM}}{R}$

View answer & explanation

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:

$v_e = \frac{\sqrt{2GM}}{R}$

39.

Which of these is a derived unit?

A.

Kilogram

B.

Metre

C.

Newton

D.

Second

View answer & explanation

Correct answer is C

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

40.

In which of the following situations is friction not useful?

A.

Operation of a grinding machine

B.

Walking

C.

Application of brakes

D.

Moving piston in a sleeve

View answer & explanation

Correct answer is D

friction, force that resists the sliding or rolling of one solid object over another.

Examples of friction in our daily life

Driving of a a vehicle on a surface.
Applying brakes to stop a moving vehicle.
Skating.
Walking on the road.

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