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# 11 Balder - stora krönet

Do you see how the large hill in Balder looks like the parabolic path e.g. of a ball. While the ball is in flight, it is only influenced by gravity. In the same way, those who travel in the Balder train will feel weightless if the train has the right speed. How long time can you be weightless in Balder - and what speed is required by the train in the highest point?

The wooden beams give Balder a coordinate system of its own. The distance between the horizontal beams is about 250 cm, while the distance between the vertical beams is slightly longer, about 275 cm. Use the image to estimate the height, h, of the part of the track that resembles a parabola.

• How long time would it take for a ball in free fall to move up that height and then come back down again? (Remember the relation h=gt2/2 for the time to fall a distance h from the highest point.)
• How far does the train travel during the time it moves up and down over this part of the large hill?

The graph below shows the variation of the G force while you move over the hill if you travel in the middle of the train (row 8). (The image below shows the photo with the coordinate system overlaid).

Do you calculations agree with the graph?

How do you think that the graph will be modified if you sitt in the front or back of the train? (See a comparison)