9th Class Science Sample Paper Sample Paper - 1 Term - 1

  • question_answer 34) State the law of conservation of momentum. Derive it by using Newton's third law of motion. Or (i) What is inertia? Among three solid balls made up of aluminum, steel and wood of same shape and volume, which of them would have highest inertia? Why? (ii) Describe in brief an activity to illustrate the property of inertia of rest.  


    It states if no external force acts on a system of particles, the algebraic sum of the linear momentum of particles remains conserved. Suppose two objects A and B of masses  and  are travelling in same direction along a straight line at velocities  and  respectively. They will collide if Let after collision, the final velocities of A  and B become andrespectively. They will separate after collision, if                                                                                                                                                                                                                         (2)        Now, initial momentum of particle Initial momentum of particle Final momentum of particle Final momentum of particle Rate of change of momentum of particle, A           ?(i) Rate of change of momentum of particle, B       ?(ii) Let and be the force exerted by particle B on A and particle A on B respectively.                                                                (1) Then by Newton's second law We have, and        Then by Newton's third law, we have This gives             or                            or Initial momentum of the system = Final momentum of the system. It is the law of conservation of momentum.                                                                                                                                        (2) OR (i) Inertia is the property of a body by virtue of which it remains in a state of rest or of uniform motion until unless acted upon by an external force. Since, steel has more density and hence more mass than the other three. Therefore, steel ball will have more inertia.                                                                                                                                   (1) (ii) Activity to show the property of inertia of rest Place a one rupee coin on a stiff playing card covering an empty glass tumbler kept on a table as shown below. Give the card a sharp horizontal flick with a finger. The card shoots away allowing the coin to fall vertically into the glass tumbler due to inertia of rest.                                                                                                                                                    (1) Here in this activity the inertia of coin Trier to maintain its state of rest even when the card blows off.                    (1)  



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