h 54 Changes in energy and momentum Two identical pucks slide across a level, fr
ID: 2036711 • Letter: H
Question
h 54 Changes in energy and momentum Two identical pucks slide across a level, frictionless table. Initially, the pucks have the same speed, but their velocities are perpendicular to each other as shown. 2. The same constant force is exerted on each puck for the same interval of time: from the instant shown until puck 1 crosses the second dotted line. The pucks remain on the table and do not collide during this time interval. 02 when puck l crosses the second dotted line, is puck 2 to the left or to the right of, or crossing the second dotted line? Explain how you can tell. a. In the diagram above, sketch the trajectory of each of the pucks. Explain how you decided to draw the trajectories the way you did. b. When puck 1 crosses the second dotted line, is the magnitude of its momentum greater than less than, or equal to the magnitude of the momentum of puck 2 at the same instant? Explain the reasoning you used in making this comparison. c. When puck 1 crosses the second dotted line, is the kinetic energy of puck 1 greater than, less than, or equal to the kinetic energy of puck 2 at the same instant? Explain the reasoning you used in making this comparison.Explanation / Answer
a)
inital momentum of puck 1 = mv1i
initial momentum of puck 2 = mv2i
Foce applied on each puck = F
let t be the intervel of the force then
momentum imparted to each puck = Ft
Puck1 has an inital velocity towards the second dotted lie ( we take it as x )
initla velocity of puck2 along x =0
hence puck 2 remains to the left of the dotted line by the time puck1 crosses the line.
b) total momentum of Puck1 when crossing the dotted line
p1 = mv1i + Ft in x-dir
total momentum of puck2 = mv2i - y-dr
= Ft - x-dir
magnitude of total mometum of puck2 p2 = sqrt( mv2i2 + (Ft)2 )
mv1i = mv2i
p1/p2 >1
mag. of momentum of puck1 > mag. momentum of puck2.
c) KE = p2/2m
K1/K2 = p12 /p22 >1
hence KE of puck1 is greater than that of puck2
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