A classical mechanics problem by Kishor Neupane

Classical Mechanics Level pending

  1. A force applied to a body of mass 0.5kg for 2 sec which is moving with velocity of 8m/s changes the direction of motion by angle of 60 degree.the force is?

  2. A force applied to a bodyof mass 0.5kg for 2 sec which is moving with velocity of 10m/s 37 degree north of east changes the velocity finally to travel along north.the force is?

my teacher said q no 1. cannot be solved using components but q no 2 can be solved using components.why is that and please give the solutions to the problems please. Thank you!

ans given is for both questions which is same.


The answer is 2.

Kishor Neupane by Kishor Neupane , 25, Nepal

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2 solutions

Ronak Agarwal
Jun 10, 2014

P l e a s e n o t e t h a t a n s w e r o f Q . 2 i s 5 n o t 2. I t e l l y o u h o w . v i = 8 i + 6 j . v f = 10 j . S o w e c a n s a y t h a t v f − v i = a t = − 8 i + 4 j . N o w s i n c e t = 2 s e c h e n c e a = − 4 i + 2 j = 4 2 + 2 2 = 2 5 . M u l t i p l y i n g b y m a s s 0.5 k g w e g e t F = 5 N . Please\quad note\quad that\quad answer\quad of\quad Q.2\quad is\quad \sqrt { 5 } \quad not\quad 2.\\ I\quad tell\quad you\quad how.\quad { v }_{ i }=\quad 8i+6j.\quad { v }_{ f }=10j.\quad So\quad we\quad can\quad say\quad \\ that\quad { v }_{ f }-{ v }_{ i }=at=-8i+4j.\quad Now\quad since\quad t\quad =2\quad sec\quad hence\\ a=-4i+2j=\sqrt { { 4 }^{ 2 }+{ 2 }^{ 2 } } =2\sqrt { 5 } .Multiplying\quad by\quad mass\quad 0.5\\ kg\quad we\quad get\quad F=\sqrt { 5 } N.

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Devesh Tripathi
Jun 12, 2014

F=(Pf-Pi)/t Pi= 4i^ Pf= 4cos 60 i^ + 4sin 60 j^ t=2 Put the values nd find the magnitude of F vector to get the desired result....

I hav solved dis que using components so i reckon ur teacher ws wrng if he says we can't solve the frst one using components...

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