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graveyarddreams
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#1
Report Thread starter 13 years ago
#1
a coin is projected with speed 6m/s along the horizontal surface of a beach. the coefficent of friction between the coin and the surface is 0.7. Modelling the coin as a particle and assuming no air resistance, find the speed of the coin after 0.3s.
(can someone work this through in detail for me?)
thanks and reps! btw the answer is 3.94m/s.
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Evil Phoenix
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Report 13 years ago
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alright

coeff of friction = friction/reaction force
the force on the coin is the friction, therefore F =ma (mass times acceleration)

since reaction force is = to weight u can substitute in the equation of friction/reaction force (F/R)

ma/mg = 0.7

ms cancel out, ur left with a/g = 0.7

g= 9.81,
multiply 9.81 by .7 and u get -6.867 (acceleration must be negative since force is backwards)

then u work out the change in velocity (time x acceleration) = 0.3 x 6.867

which gives u 2.0601

then u subtract that from 6 and u get 3.9399 which is ≈ 3.94


hope that helped
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Evil Phoenix
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#3
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and dont worry about givin me rep,
it wud b prety much cheating
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graveyarddreams
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#4
Report Thread starter 13 years ago
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thanks!! yeah i understand now, it's not hard except realising the first bit. *reps*
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Evil Phoenix
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#5
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awwww u didnt need to... but thanx
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