JAMB Physics Past Questions & Answers - Page 221

1,101.

The total length of a spring when a mass of 20g is hung from its end is 14cm, while its total length is 16cm when a mass of 30g is hung from the same end. Calculate the unstretched length of the spring assuming Hooke's law is obeyed.

A.

9.33cm

B.

10.00cm

C.

10.66cm

D.

12.00cm

E.

15.00cm

Correct answer is B

Let unstretched length = L

e1 = 14 - L and e2 = 16 - L

Using, \(\frac{m_1}{e_1}\) = \(\frac{m_2}{e_2}\)

\(\frac{20}{14 - L}\) = \(\frac{30}{16 - L}\)

L = 10cm

1,102.

1,000 identical drops of oil of density 500kgm-3 have a total mass of 5 x 10-4kg. One of the drops forms a thin film of area 0.5m2 on water. The thickness of the film is

A.

2 x 10-8m

B.

2 x 10-9m

C.

2 x 10-7m

D.

3 x 10-9m

E.

2.8 x 10-8m

Correct answer is B

Mass of one oil = \(\frac{5 \times 10^{-4}}{1000}\)

= 5 x 10-4kg

Density = \(\frac{\text {mass}}{\text{area x thickness}}\)

500 = \(\frac{5 \times 10^{-7}}{\text{0.5 x thickness}}\)

thickness = 2 x 10-9m

1,103.

A force of 16N is applied on a 4.0kg block that is at rest on a smooth, horizontal surface. What is the velocity of the block at t = 5 seconds?

A.

4ms-1

B.

10ms-1

C.

20ms-1

D.

50ms-1

E.

80ms-1

Correct answer is C

F = ma

= \(\frac{m(u - v)}{t}\)

16 = \(\frac{4(v - 0)}{5}\)

v = 20ms-1

1,104.

Of the following derived units, the one that is not a unit of power is

A.

joule/second

B.

ampere volt

C.

ampere2volt

D.

volts2/ohm

Correct answer is C

Power = \(\frac{Work done}{time}\) = \(Js^{-1}\)

Power = \(current \times voltage\) = \(Ampere volt\)

Power = \(\frac{voltage^{2}}{resistance}\) = \(\frac{volts^{2}}{ohm}\)

 

1,105.

The electrochemical equivalent of a metal is 0.126 x 10-6 kgC-1. The mass of the metal that a current of 5A will deposit from a suitable bath in 1 hour is

A.

0.0378 x 10 -3kg

B.

0.227 x 10 -3kg

C.

0.378 x 10 -3kg

D.

0.595 x 10 -3kg

E.

2.268 x 10 -3kg

Correct answer is E

m = Itz

= 5 x 3600 x 0.126 x 10-6

= 2.268 x 10-3kg