First slide
Third law

An explosion breaks a rock into three parts in a horizontal plane. Two of them go off at right angles to each other. The first part of mass 1 kg moves with a speed of12  ms1and the second part of mass 2 kg moves with 8  ms1speed. If the third part flies off with4  ms1speed, then its mass is


The situation is as shown in the figure.

According to law of conservation of linear momentum

p¯1+p¯2+p¯3=0     p¯3=p¯1+p¯2 Here p¯1=1kg12ms1i^=12i^kgms1 p¯2=2kg8ms1j^=16j^kgms1   p¯3=12i^+16j^kgms1 The magnitude of p¯3 is p¯3=122+162=20kgms1   m3=p3v3=20kgms14ms1=5kg

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