JAMB Physics Past Questions 2021

10 questions from the JAMB 2021 Physics paper, with answers and explanations. Tap "Show answer" under each one when you are ready.

JAMB 2021Question 1 · Electronics and Alternating Current

In a series R-L-C circuit at resonance, the voltages across the resistor and the inductors are

30 V

and

40 V

respectively. What is the voltage across the capacitor?

A. $30 V$
B. $40 V$
C. $50 V$
D. $70 V$

Show answer

Answer: B. $40 V$

At resonance, VL=VC, so the capacitor voltage is $40 V$ .

JAMB 2021Question 2 · General Physics and Measurement

The inner diameter of a test tube can be measured accurately using a?

A.micrometer screw gauge
B.pair of dividers
C.meter rule
D.pair of vernier calipers

Show answer

Answer: D. pair of vernier calipers

A pair of vernier calipers accurately measures the inner diameter of a test tube.

JAMB 2021Question 3 · Heat and Thermodynamics

Calculate the heat energy required to vaporize

50 g

of water initially at

8 0^{\circ} C

if the specific heat capacity of water is 4.23jg

^{- 1}

^{- 1}

(specific latent heat of vaporization of water is 2260jg

^{- 1}

A. $530000 J$
B. $23200 J$
C. $17200 J$
D. $130000 J$

Show answer

Answer: D. $130000 J$

Heating to $100 C$ then vaporizing gives about $117, 230 J$ , closest to $130, 000 J$ .

JAMB 2021Question 4 · Heat and Thermodynamics

The temperature gradient across a copper rod of thickness

0.02 m

, maintained at two temperature junctions of

2 0^{\circ}

and

8 0^{\circ} C

respectively is?

A. $3.0 \times 1 0^{2}$ $k m^{- 1}$
B. $3.0 \times 1 0^{3}$ $k m^{- 1}$
C. $5.0 \times 1 0^{3}$ $k m^{- 1}$
D. $3.0 \times 1 0^{4}$ $k m^{- 1}$

Show answer

Answer: B. $3.0 \times 1 0^{3}$ $k m^{- 1}$

Gradient=(80-20)/0.02= $3000 K m^{- 1}$ .

JAMB 2021Question 5 · Mechanics, Motion, and Energy

The motion of a body is simple harmonic if the?

A.acceleration is always directed towards a fixed point
B.path of motion is a straight line
C.acceleration is proportional to the square of the distance from a fixed point
D.acceleration is constant and directed towards a fixed point

Show answer

Answer: A. acceleration is always directed towards a fixed point

In SHM, the acceleration is always directed towards a fixed point (and proportional to displacement).

JAMB 2021Question 6 · Mechanics, Motion, and Energy

A ball of mass

0.1 kg

is thrown vertically upwards with a speed of

10 m s^{- 1}

from the top of a tower

10 m

high. Neglecting air resistance, its total energy just before hitting the ground is? (Take g =

10 m s^{- 2}

)

A. $5 J$
B. $10 J$
C. $15 J$
D. $20 J$

Show answer

Answer: C. $15 J$

Total mechanical energy=initial KE+initial PE=5+10= $15 J$ .

JAMB 2021Question 7 · Nuclear and Modern Physics

If the fraction of the atoms of a radioactive material left after 120 years is

\frac{1}{64}

, what is the half-life of the material?

A.24 years
B.20 years
C.10 years
D.2 years

Show answer

Answer: B. 20 years

6 half-lives=120 years, so the half-life is 20 years.

JAMB 2021Question 8 · Properties of Matter and Fluids

If the stress on a wire is 10

^{7}

^{- 2}

and the wire is stretched from its original length of

10.00 m

10.05 m

. The young's modulus of the wire is?

A. $5.0 \times 1 0^{- 4}$ Nm $^{- 2}$
B. $5.0 \times 1 0^{- 5}$ Nm $^{- 2}$
C. $2.0 \times 1 0^{- 8}$ Nm $^{- 2}$
D. $2.0 \times 1 0^{9}$ Nm $^{- 2}$

Show answer

Answer: D. $2.0 \times 1 0^{9}$ Nm $^{- 2}$

Young's modulus=stress/strain= $1 0^{7}$ /( $\frac{0.05}{10}$ )= $2.0 \times 1 0^{9}$ $N m^{- 2}$ .

JAMB 2021Question 9 · Waves, Sound, and Optics

A boy standing some distance from the foot of a tall cliff claps his hands and hears an echo

0.5 s

later. If the speed of sound is

340 m s^{- 1}

, how far is he from the cliff?

A. $680 m$
B. $170 m$
C. $34 m$
D. $85 m$

Show answer

Answer: D. $85 m$

distance=vxt/2=340x0.5/2= $85 m$ .

JAMB 2021Question 10 · Waves, Sound, and Optics

A man stands

4 m

in front of a plane mirror. If the mirror is moved

1 m

towards the man, the distance between him and his new image is?

A. $3 m$
B. $5 m$
C. $6 m$
D. $10 m$

Show answer

Answer: C. $6 m$

With the mirror $3 m$ from the man, the image is 2x3= $6 m$ away.

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