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Help, Physics energy question

SeraphthroneSeraphthrone Registered User Posts: 339 Member
edited December 2005 in AP Tests Preparation
a mass of 12kg is placed on an incline angled at 30 degrees from the horizontal. a spring that can be compressed 2 cm by a force of 270N is placed on the incline below the mass. the mass is released and hit the spring and momentarily stops when it compressed the spring by 5.5 cm. how far has the mass moved down the incline? why is the speed of the mass when it hits the spring?

the correct answer for the first question is 35cm
answer for second question is 1.7m/s

I worked it out but got the wrong answer. my calulation is like below:

Energy of spring = kx^2 = 270N/2cm * 5.5cm * 0.055m = 40.83J
Energy of spring = kinetic energy = (m * v^2) / 2.
solve for v i got 2.608 (the correct answer is 1.7)

Kinetic energy = the work done on the mass by the component of gravity
= F * d = 9.8 * 12 * cos60 * d
solve for d I got 0.694m (correct answer 0.35m)

wut did i do wrongly??

plz help me
Post edited by Seraphthrone on

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