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a ball with the mass of 50 grams hangs on a very light thread who has the lenght of 80 cm and swing back and forth (pendel). At the begining of the movement the maximum angle that the thread formed when moving was 35 degress, but after one minute tha angle had declined to 2o degress.The time for the ball to make one swing from its lowest point to its highest remained the same.

The question is: Is the power that the swinging energi (mekanic energi) from the pendel turns into other energi forms under one minute bigger or smaller than the averge power of the pendel?

Solution:

Well, i know how to calculate the power that turns the mekanic energi to other energiforms, its very easy. Power is P = delta E/ delta t

How much energi has the pendel lost under one minute? Tha answer to that question be found by comparing the highest level of potential energy for 35 and 20 degress. To do that you need to calculate how high the ball went from its lowest when de turning angle was 20 degress and 35 degress. That is easy to, just use basic trigonametry. When you have calculated the energ lost under one minute, get the power by using the formula P =E/60.

But as i understand it, the "average power" of the pendel is the energi amout

that turn from one form to another while the pendel swings one time from its highest point over ground to its lowest divided with the time it takes to preform the movement. To calculate this one must first calculate the speed of the pendel at the angles, divid the speed with 2, to get averege speed. ne must calculate the distance that the pendel travels by using the formula

(r*2 pi)/360 * 20 or 35. And calculate the time by dividing the distance with the average speed. When you have the time t you can calculate the power of the pendel for 20 and 35 degress. And finally calculate the "average power" of the pendel by adding the to powers for 29 and 35 degress and dividing them with two.

I have done all this, and my answer is that the average power of the pendel is much higher than the power that turns the pendels mekanic energi to other energiforms, why am i wrong? Its insane.

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A mousetrap is used as a engine for a small car with the mass of 50 gram.The car mus be able to travel 8 meters. the mousetraps arm is about 4 cm, and it can be pulled 180 degress. The force needed to pull the arm of the mousetrap is linear dependable to the turning angle. its at its lowest point 2 N and on its highest about 10 newton.

the question is: What it the maximum violocity this car can have?

Solution: The road that the "car" must travel is not of any importance.

the most important thing is to calculate how much energi can be feed into the spring of the mousetrap. You can get the violocity when you get the total energy by the formula E = 0.5 *mv^2. The distance/displacement you have to use a force F to "cock the spring" is given by a half circle, you get that by the formula 2*0.04*pi/2. The force you have to use depends of the angle. The energi used is A= F*s. Its in this case the same as the area of a

triangle with the hight 8 newton and the lenght of ( 2*0.04*pi/2). This calculation should give one the energi feed into the mousetrap spring?

And with the energi you can calculate the maximum speed.

am i wrong? Why then?