# 2019 JAMB Physics Past Questions & Answers - page 1

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1

The limiting frictional force between two surface depends on

I. the normal reaction between the surfaces

II. the area of surface in contact

III. the relative velocity between the surfaces

IV. the nature of the surface

A

I only

B

I & IV only

C

II only

D

III only

Correct Option: B

Solution

The factors that affect the friction between two surfaces are the weight of the object and the coefficient of friction of the surface. I

The interpretation of this shows that solid friction is affected by:

• The surface on which the object is moved or the nature of the surface. i.e., rough surface, smooth surface, liquids etc.
• The weight of the object or the amount of force on the surface by the object.

2

If a body moves with a constant speed and at the same time undergoes an acceleration, its motion is said to be

A

oscillation

B

circular

C

rotational

D

rectilinear

Correct Option: B

Solution

Since velocity is a vector that has both magnitude and direction, a change in either the magnitude or the direction constitutes a change in the velocity. For this reason, it can be safely concluded that an object moving in a circle at constant speed is indeed accelerating.

More

3

When blue and green colours of light are mixed, the resultant colour is

A

cyan

B

magenta

C

black

D

yellow

Correct Option: A

Solution

When green and blue lights mix, the result is a cyan. When the blue and red lights mix, the result is magenta. Red–greenblue additive mixing is used in television and computer monitors, including smartphone displays, to produce a wide range of colors. A screen pixel uses a juxtaposition of these three primary colors.

via wikipedia

4

A metal rod has a length of 100cm at 200$$^oC$$. At what temperature will its length be 99.4cm. If the linear expansivity of the material of the rod is 2 x 10$$^{-5}C^{-1}$$

A

200$$^o$$C

B

300$$^o$$C

C

100$$^o$$C

D

-100$$^o$$C

Correct Option: D

Solution

L$$_1$$ = 100cm,

T$$_1$$ = 200$$^o$$C

L$$_2$$ = 99.4cm,

T$$_2$$ = ?

$$\alpha$$ = 2 x 10$$^{-5}$$C$$^{-1}$$

$$\alpha$$ = $$\frac{L_2 - L_1}{L_1(T_2 - T_1)}$$

2 x 10$$^{-5} = \frac{100- 99.4}{100(200 - T_2)} = \frac{0.6}{100(200 - T_2)}$$

2 x 10$$^{-5}$$ x $$100(200 - T_2) = 0.6$$

$$200 - T_2 = \frac{0.6}{0.002} = 300^oC$$

$$T_2 = 200 - 300 = -100^oC$$

5

According to kinetic molecular model, in gases

A

The molecule are very fast apart & occupy all the space made available

B

A. The particles vibrate about fixed positions and are held together by the strong intermolecular bond between them

C

B. The particles occur in clusters with molecules slightly farther apart

D

The particles are closely packed together, they occupy minimum space & are usually arranged in a regular pattern

Correct Option: A

Solution

In kinetic molecular theory, the gases are energised and hence moves freely and energetically as they occupy specific space.

Kinetic Molecular Theory states that gas particles are in constant motion and exhibit perfectly elastic collisions. Kinetic Molecular Theory can be used to explain both Charles' and Boyle's Laws. The average kinetic energy of a collection of gas particles is directly proportional to absolute temperature only.

6

The value of T in the figure above is

A

30N

B

10.0N

C

20N

D

40N

Correct Option: D

Solution

Formula:

Tsin30 + Tsin30 = 40

2Tsin30 = 40

Tsin30 = 40/2 = 20

T($$\frac{1}{2}$$) = 20

T = 20 x 2

T = 40N

7

A train has an initial velocity of 44m/s and an acceleration of -4m/s$$^2$$. Calculate its velocity after 10 seconds

A

10m/s

B

6m/s

C

8m/s

D

4m/s

Correct Option: D

Solution

V = u - at,

at u = 44m/s,

44 + [-4]10

4m/s

8

Lamps in domestic lightings are usually in

A

series

B

divergent

C

convergent

D

parallel

Correct Option: D

Solution

The arrangement of the lamps in lightenings is such that heat losses are reduced. The resultant resistance is small for a parallel arrangement which means there is low heat losses: [Heat $$\alpha$$ R]

9

During the transformation of matter from the solid to the liquid state, the heat supplied does not produce temperature increase because

A

all the heat is used to break the bonds holding the molecules of the solid together

B

the heat capacity has become very large as the substance melts

C

the heat energy is quickly conducted away

D

the heat gained is equal to the heat lost by the substance

Correct Option: A

Solution

The change from the solid-state to the liquid state is called melting. The temperature at which a substance changes from a solid to a liquid is called the melting point. During this transformation process from the solid to the liquid state, there is no production of temperature increase due to the heat supplied because all the heat is used to break the bonds holding the molecules of the solid together

10

In a slide wire bridge, the balance is obtained at a point 25cm from one end of wire 1m long. The resistance to be tested is connected to that end and a standard resistance of 3.6$$\Omega$$ is connected to the other end of the wire. Determine the value of the unknown resistance

A

3.2$$\Omega$$

B

1.4$$\Omega$$

C

3.21$$\Omega$$

D

1.2$$\Omega$$

Correct Option: D

Solution

$$\frac{R}{3.6} = \frac{75}{25} = \frac{1}{3}$$

3R = 3.6

R = 1.2$$\Omega$$

Answer: 1.2$$\Omega$$

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