Fundamental Forces in Nature - UNSOLVED PRACTICE SET

Q7. Name the four fundamental forces in nature and arrange them in order of increasing relative strength.

Q8. Why is the gravitational force called a "universal" force? Explain why it is the weakest yet most far-reaching force.

Q9. What is the strong nuclear force? Why is it necessary to explain the stability of atomic nuclei?

Q10. A student drops a book and a magnet from the same height. Both fall due to gravity, but the magnet also attracts a paperclip. Compare the fundamental forces involved in these two observations.

Q11. The weak nuclear force is responsible for certain types of radioactive decay. Explain why this force is called "weak" despite playing a crucial role in stellar processes like the Sun's energy production.

Q12. Why do we not feel the strong nuclear force in our everyday experiences, even though it is the strongest of all fundamental forces?

Q13. Compare the four fundamental forces of nature on the basis of:

(i) Relative strength

(ii) Range of operation

(iii) Nature of interaction (attractive/repulsive)

(iv) Particles that mediate the force

(v) Examples from nature

Q14. Discuss the unification of forces in nature. How did Newton unify terrestrial and celestial mechanics? How did Maxwell unify electricity and magnetism? What is the current status of the Grand Unified Theory (GUT)?

Q15. The Sun shines because of nuclear fusion, where hydrogen nuclei combine to form helium. Analyse the role of the strong nuclear force and the electromagnetic force in this process. Why does the strong nuclear force "win" over the electromagnetic repulsion between protons inside the Sun's core?

Q16. The gravitational force between two 1 kg masses placed 1 metre apart is approximately 6.67 × 10⁻¹¹ N. The electrostatic force between two protons placed at the same distance is approximately 2.3 × 10⁻²⁸ N (repulsive). Wait — actually, the Coulomb force between two protons 1 metre apart is about 2.3 × 10⁻²⁸ N? No, recalculate: the Coulomb force between two protons separated by 1 metre is given by kq²/r² where k = 9 × 10⁹ Nm²/C² and q = 1.6 × 10⁻¹⁹ C.

(a) Calculate the actual electrostatic force between two protons 1 metre apart.

(b) Compare this with the gravitational force between two protons at the same distance (mass of proton = 1.67 × 10⁻²⁷ kg, G = 6.67 × 10⁻¹¹ Nm²/kg²).

(c) By what factor is the electromagnetic force stronger than the gravitational force? What does this comparison tell us about the relative strengths of these forces?

Q17. In a nuclear reactor, a neutron is absorbed by a uranium-235 nucleus, causing it to split. The strong nuclear force acts between nucleons (protons and neutrons) with a range of about 1–3 femtometres (1 fm = 10⁻¹⁵ m). 

(a) Explain why the strong force does not act between the nucleus and electrons in the atom.

(b) If the diameter of a uranium nucleus is about 15 fm, calculate how many times smaller this is compared to the diameter of the atom (about 10⁻¹⁰ m).

Q18. A student is trying to understand why a table feels solid even though atoms are mostly empty space. The electromagnetic repulsion between electron clouds of atoms prevents your hand from passing through the table. 

(a) Identify the fundamental force responsible for this everyday experience.

(b) Explain why the gravitational force between your hand and the table is negligible in this situation.

(c) If the mass of your hand is 0.5 kg and the mass of the table is 20 kg, and they are 0.01 m apart, calculate the gravitational force between them. (G = 6.67 × 10⁻¹¹ Nm²/kg²)

(d) What does this tell you about why we don't "feel" gravity in everyday contact forces?