JAMB Physics Past Questions & Answers - Page 149

741.

A force of 100N was used to kick a football of mass 0.8kg. Find the velocity with which the ball moves if it takes 0.8s to be kicked

A.

\(32ms^{-1} \)

B.

\(50ms^{-1} \)

C.

\(64ms^{-1} \)

D.

\(100ms^{-1} \)

Correct answer is D

From Newton's second law:

\( F = \frac{mV - mµ}{t} \)

Let the final velocity = V; and since the football is initially at rest, its initial vel µ = 0, M = 0.8kg

\( t = 0.8s \\

\implies 100 = \frac{0.8V - 0.8 \times 0}{0.8} \\

\text{Therefore } V = \frac{100 \times 0.8}{0.8} = 100ms^{-1} \)

742.

An electron makes a transition from a certain energy level Ek to the ground state E0. If the frequency of emission is 8.0 x 1014Hz The energy emitted is

A.

8.25 x 10-19J

B.

5.28 x 10-19J

C.

5.28 x 1019J

D.

8.25 x 1019J

Correct answer is B

Atomic emission and absorption of energy is usually in packets referred to as photon or quantum of energy of magnitude E =hf, where f is the frequency and h is the plancks constant

Energy emitted = hf

= 6.6 x 10-34 x 8.0 x 10-14
= 5.28 x 10-19J

743.

In the calibration of an ammeter using faraday's laws of electrolysis, the ammeter reading is kept constant at 1.2A. If 0.990g of copper is deposited in 40 minutes , the correction to be applied to the ammeter is

A.

0.03A

B.

0.04A

C.

0.05A

D.

0.06A

Correct answer is C

From faraday's law of electrolysis

M = I t Z
0.990 = I x (40 x 60) x 3.3 x 10-4

\( \implies \frac{0.990}{2400 \times 3.3 \times 10^{-4}} = 1.25A \\
\text{Thus the correction to be made } = 1.25 - 1.20 = 0.05A \)

744.

A ray of light is incident on an equilateral triangular glass prism of refractive index 3/2, Calculate the angle through which the ray is minimally deviated in the prism

A.

30.0\(^{\circ} \)

B.

37.2\(^{\circ} \)

C.

42.0\(^{\circ} \)

D.

48.6\(^{\circ} \)

Correct answer is B

For the equilateral glass prism A = 600

\( \frac{3}{2} \text{Sin} \frac{\left( \frac{Dm + 60}{2}\right)}{\left(\frac{60}{2}\right)}= \frac{\left( \text{ Sin }\frac{Dm + 60}{2} \right)}{0.5} \\

\implies Dm = 37.2^{\circ} \)

745.

A bead traveling on a straight wire is brought to rest at 0.2m by friction. If the mass of the bead is 0.01kg and the coefficient of friction between the bead and the wire is 0.1 determine the work done by the friction

A.

\( 2 \times 10^{-4}J \)

B.

\( 2 \times 10^{-3}J \)

C.

\( 2 \times 10^{1}J \)

D.

\( 2 \times 10^{2}J \)

Correct answer is B

Work done by friction = Friction force x Displacement from the relation, f = uR

where u = coefficient of friction; R= Normal reaction

F = u mg (R =mg)
= 0.1 x 0.01 x 10
work done = F x Displacement
= 0.1 x 0.01 x 10 x 0.2
= 0.002 or \( 2 \times 10^{-3}J \)