question_answer

  (i) Explain why is it difficult to walk on sand? (ii) Why is the recoil of a heavy gun, on firing, not so strong as that of a light gun using the same cartridge? (iii) A constant force acts on an object of 5kg for a period of 2 s. It increases the velocity of an object from 3 m/s to7 m/s. Find the magnitude of the applied force. Now if the force was applied for a period of 5 s, what would be the final velocity of the object? Or (a) Derive an expression to prove the law of conservation of momentum. (b) Why does a karate expert suddenly reduce the speed of his hand while striking a slab of ice? Explain with reference to Newton's law of motion.

Answer:

  (i) While walking on sand, the sand gets pressed down, impacting less reaction force on the person.       (1) (ii) The mass of the gun is higher. So, it coil's velocity is less.                                                                                         (1) (iii) Given,                                                                                                                                                                            (1)