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physicsgirl · Oct 14, 2007, 01:54 PM

A wooden block with mass 1.55 kg is placed against a compressed spring at the bottom of a slope inclined at an angle of 32.0 degrees (point A). When the spring is released, it projects the block up the incline. At point B, a distance of 4.45 m up the incline from A, the block is moving up the incline at a speed of 5.75 m/s and is no longer in contact with the spring. The coefficient of kinetic friction between the block and incline is 0.45. The mass of the spring is negligible.

Calculate the amount of potential energy that was initially stored in the spring.
Take free fall acceleration to be 9.80 m/s^2.

Can someone please help me with this? I have no idea how to do it. Thanks!

terryg752 · Oct 14, 2007, 02:44 PM

I will give you some hints to solve the question:

The potential energy of the spring = initial kinetic energy to th block.

If the block has initial velocity v, and mass m, its kinetic energy = 1/2 mv^2

Now its initial velocity is v

Forces acting on it are: its weight downward, normal reaction of block perpendicular
to the incline, and friction with direction downward along the incline.

Friction = Normal reaction times coefficient of friction

You have to find the net force acting on the block downward along the incline.

Divide this net force by mass to get acceleration.

Use the distance (4.45), final velocity (5.75), and acceleration to find the initial velocity v

From v calculate initial kinetic energy.

This is equal to potential energy.