A wooden block with mass 1.20 kg is placed against a compressed spring at the bo

Question

A wooden block with mass 1.20 kg is placed against a compressed spring at the bottom of a slope inclined at an angle of 35.0 (point A). When the spring is released, it projects the block up the incline. At point B, a distance of 5.55 m up the incline from A, the block is moving up the incline at a speed of 6.70 m/s and is no longer in contact with the spring. The coefficient of kinetic friction between the block and incline is k = 0.45. The mass of the spring is negligible. Part A Calculate the amount of potential energy that was initially stored in the spring.

Explanation / Answer

Initial potential energy = work done against friction+ increases in gravitational potential energy and kinetic energy.

= mg (cos ) x d + mg d sin + (1/2) mv²

=(0.45 x 1.2 x 9.8 (cos 35 ) x 5.55 ) + (1.2 x 9.8 x 5.55 x sin 35) + ( 0.5 x 1.2 x 6.72 )
= 24.1 + 37.4 + 26.9 = 88.4 J

Amount of potential energy stored in the spring initially is = 88.4 J   

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