Une plateforme à roulettes de 48 kg est accrochée à un ressort horizontal dont la constante de rappel est de 20 N/m : l'autre extrémité du ressort est fixée au mur. Le frottement entre la plate-forme et le plancher est négligeable. On éloigne la plate-forme du mur afin d'allonger le ressort de 1.5 m, puis on la lâche (vitesse initiale nulle). Béatrice, dont la masse est de 65 kg, marche à côté de la plate-forme en s'efforçant d'aller à la même vitesse ; quand la plate-forme est au centre de l'oscillation, elle monte dessus. Calculez l'énergie mécanique de Béatrice et de la plate-forme avant qu'elle n'y monte.

An alligator swims to the left with a constant velocity of 5 \,\dfrac{\text{m}}{\text s}5 s m ? 5, space, start fraction, m, divided by, s, end fraction. when the alligator sees a bird straight ahead, the alligator speeds up with a constant acceleration of 3 \,\dfrac{\text {m}}{\text s^2}3 s 2 m ? 3, space, start fraction, m, divided by, s, start superscript, 2, end superscript, end fraction leftward until it reaches a final velocity of 35 \,\dfrac{\text {m}}{\text s}35 s m ? 35, space, start fraction, m, divided by, s, end fraction leftward. how many seconds does it take the alligator to speed up from 5 \,\dfrac{\text {m}}{\text s}5 s m ? 5, space, start fraction, m, divided by, s, end fraction to 35 \,\dfrac{\text {m}}{\text s}35 s m ? 35, space, start fraction, m, divided by, s, end fraction?

An initially unpolarized light if intensity 500 w/m^2 passes through four polarizers. the transmission axis between adjacent polarizers is 45∘. what percentage of the initial intensity is transmitted by the system?

Total solidification times of three casting geometries are to be compared: a sphere, a cylinder, in which the length-to-diameter ration - 1.0, and a cube. volume = 1000 cm^3 for all three shhapes, and the same casting alloy is used. a) determine the solidification times of each geometry b) based on the results of part (a), which geometric element would make the best riser? c) if the mold constant = 3.5 min/cm^2 in chvorinov's rule, compute the total solidification time for each casting.