1.A ball mass 200g traveling at 5m/s collides elastically withanother ball trave

Question

1.A ball mass 200g traveling at 5m/s collides elastically withanother ball traveling in the opposite direction at 2m/s. Ifthe first ball ends up traveling in the opposite direction at 2m/sthen the mass of the second ball is: a) 100g   b)200g   c) 250g   d) 500g 2. An object mass 10kgtraveling with a velocity of 20m/s collides head on and elasticallywith a stationary object of mass 2kg. The velocities of firstand second objects after the collision are: a) 0m/s and20m/s b) 0m/s and 100m/s c) 13 m/s and 33 m/s d)16m/s and 20m/s 1.A ball mass 200g traveling at 5m/s collides elastically withanother ball traveling in the opposite direction at 2m/s. Ifthe first ball ends up traveling in the opposite direction at 2m/sthen the mass of the second ball is: a) 100g   b)200g   c) 250g   d) 500g 2. An object mass 10kgtraveling with a velocity of 20m/s collides head on and elasticallywith a stationary object of mass 2kg. The velocities of firstand second objects after the collision are: a) 0m/s and20m/s b) 0m/s and 100m/s c) 13 m/s and 33 m/s d)16m/s and 20m/s

Explanation / Answer

a)as the momentum is conserved we have

let the mass of the second ball is m

we have 0.2*5-2m=mv-0.2*2

and we have as e=1    5+2=v+2  v=5m/sec

we have m=0.2kgs

v1=[m1-m2]u1/[m1+m2 ] +    [2m2u2/m1+m2]
v2=[m2-m1]u2/[m1+m2] +    [2m1u1/m1+m2]

this is the formula for two objects colliding elastically

there is another way to solve this that is the velocities areexchanged

implies they have same mass

b)10*20=2*v2+10*v1     v2-v1=20m/sec

solving we get the option c 33 and 13m/sec

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