# 2020 - JAMB Physics Past Questions and Answers - page 1

A few grains of table salt were put in a cup of cold water, kept at constant temperature and left undistributed. Eventually all the water tested salty. This action is due to?

convection

osmosis

capillarity

diffusion

**correct option:**c

Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity.

The force required to make an object of mass m, travelling with velocity v, turn in a circle of radius r is

\(\frac{mv^2}{r}\)

\(\frac{mr^2}{x}\)

\(\frac{mr}{v}\)

\(\frac{mv}{r^2}\)

**correct option:**a

A machine gun with a mass of 5kg fires a 50g bullet at a speed of 100 ms\(^{-1}\). The recoil speed of the machine gun is

0.5 ms\(^{-1}\)

1.5 ms\(^{-1}\)

1 ms\(^{-1}\)

2ms\(^-1\)

**correct option:**c

Gun momentum = bullet momentum

M\(_a\)V\(_a\) = M\(_b\)V\(_b\)

5 x V\(_a\) = 0.05 x 100

V\(_a\) = 1m\(^{-1}\)

If in a simple pendulum experiment the length of the inextensible string is increased by a factor or four, its period is increased by a factor of?

4

\(\frac{\pi}{2}\)

\(\frac{1}{4}\)

2

**correct option:**d

For a simple pendulum, T = 2\(\pi\)\(\sqrt{\frac{L}{g}}\)

\(\frac{T_1}{T_2} = \sqrt{\frac{L_1}{L_2}}\) but L\(_2\) = 4L\(_1\)

\(\frac{T_1}{T_2} = \sqrt{\frac{L_1}{4L_1}}\)

T\(_2\) = 2T\(_1\)

In what range of temperature is the expansion of water anomalous?

+208\(^o\)C to +212\(^o\)C

-80\(^o\)C + -76\(^o\)C

0\(^o\)C to +4\(^o\)C

-4\(^o\)C to +0\(^o\)C

**correct option:**c

The **anomalous expansion of water** is an abnormal property of **water** whereby it expands instead of contracting when the temperature goes from 0\(^o\)C to +4\(^o\)C, and it becomes less dense

Which of the following statements about radioactivity is true?

(i) Alpha particle is positively charged

(ii) Beta particle is negatively charged

(iii) Gamma ray is neutral

(iv) Beta particle has the same mass as helium atom

(v) Gamma ray is charged.

i, ii, iii, iv only

i, ii, iii only

iv and v only

i, ii and v only

**correct option:**b

In the study of Physics, temperature and heat are often confused with each other. Which of the following statements correctly defines these two elements?

Temperature is a measure of the average kinetic energy of the molecules of a substance

Heat is a measure of the total kinetic energy of the molecules in a system

Different materials require different amounts of heat to cause a given change in temperature

All of the above

**correct option:**d

The effect of closing the key K in the circuit shown in the figure above would be to?

increase the current by 0.4A

reduce the current by 0.4A

increase the current by 0.6A

reduce the current by 0.6A

**correct option:**a

When K is open, the total Resistance = 8 + 2 = 10\(\Omega\)

1 = \(\frac{V}{\Omega}\) = \(\frac{6v}{\Omega}\) = 0.6A

When K is closed, \(\frac{1}{8} + \frac{1}{8} = \frac{1}{\Omega}\)

\(\frac{2}{8} = \frac{1}{\Omega}\)

\(\Omega\) = \(\frac{8}{2}\) = 4\(\Omega\)

\(\Omega\) = \(\frac{8}{2}\) = 4\(\Omega\)

4\(\Omega\) in series with 2\(\Omega\)= 6\(\Omega\)

1 = \(\frac{V}{\Omega}\) = \(\frac{6}{6}\) = 1A

1 - 0.6A = 0.4A

Hence, 0.4A increase

Which of the following statements on the use of X-rays is incorrect? X-rays are used

In a hospital to obtain photographs of tissues and bones in the body

For the treatment of malignant growths like cancer cells

In detecting fingerprints

To reveal hidden flaws in metal castings and welded joints work of art

**correct option:**c

Under which of the following conditions is work done?

A boy pushes unto a table

A stands on a table

A man supports a heavy food above his head with his hands

A woman holds a pot of water