Physics Questions & Answers - Free Online Practice

3,726.

A blacksmith heated a metal whose cubic expansivity is 6.3 x 10-6K-1. The area expansivity is

2.0 x 10^-6K^-1

2.1 x 10^-6K^-1

4.2 x 10^-6K^-1

6.3 x 10^-6K^-1

View answer & explanation

Correct answer is C

If the lineal expansivity = ∝
=> area expansivity β= 2∝.
And cubic expansivity δ = 3∝.
=> 6.3 x 10-6 = 3∝
∴ ∝ =

∴ ∝ =	6.3 x 10-6	= 2.1x 10-6
	__3

∴ Area = 2∝ = 2 x 2.1x10-6
= 4.2 x 10-6K-1

3,727.

In the diagram above, a rod 50 cm long of uniform cross-section is suspended horizontally on a fulcrum, F, by the action of two forces. What is the weight of the rod?

40N

80N

120N

200N

View answer & explanation

Correct answer is B

Being a uniform rod, the height W should be acting at the mid point 25cm mark.
∴ Taking moment about the fulcrum, F,
200 x 10 = W x 10 + 40 x 30
2000 = 10W + 1200
=> 10W = 2000 - 1200
= 800
w = 800/10 = 80N

3,728.

From the diagram above, the bob of the pendulum has the fastest speed at

View answer & explanation

Correct answer is A

The ball has its fastest speed at its equilibrium position when its displacement X = 0, which is at X. At this point, the bob has maximum velocity and maximum kinetic energy.

3,729.

The figure above shows 4 forces 3N, 10N, 3√3N and 6N acting on a particle P. The resultant of he four forces is

5√ 3N

10N

10√ 3N

View answer & explanation

Correct answer is C

Resolution of force:
Total vertical upward force:
= 3√3 + 10 cos 60^o
= 3√3 + 5.
Total downward force
= 6 cos 30^o
= 6 x √(³/₂) = 3√3
Total horizontal forces towards right;
= 3N + cos 30^o
= 3N + 10 x √(³/₂)
= 3N + 5√3
Total horizontal forces towards left:
= 6 cos 60^o
= 6 x 0.5
= 3.0N
Summary:
Vertical resultant forces upward:
= 3√3 + 5 - 3√3
= 5N
Horizontal resultant forces towards right:
= 3N + 5√3 - 3√3
= 5N
Horizontal resultant force towards right
= 3N + 5√3 - 3N
= 5√3N

∴ R² = 5² + (5√3)²
= 25 + 25 x 3
= 100
∴ R = √100
= 10N

3,730.

I. High thermal capacity.
II. High sensitivity.
III.Easy readability.
IV. Accuracy over a wide range of temperature
From the statement above, the qualities of a good thermometer are

I and II

I, II,III and IV

I, III and IV

II, III and IV

View answer & explanation

Correct answer is D

A good thermometric liquid should not have a high thermal capacity so that the themperetue of the body being measured will not be affected
∴ II, III and IV are qualities of a good thermometer