3. A car is traveling at \( 15 \mathrm{~m} / \mathrm{s} \), when the traffic light 50 m ahead turns yellow. Determine the required constant deceleration of the car and the time needed to stop the car at the light.

(5) Ahmed pulls his little sister Noha in a sled on an iey surface (assume no friction), with a force of 60.0 N at an angle of \( 37.0^{\circ} \) upward from the horizontal. If he pulls her 12.0 m , what is the work done by Ahmed? \( \begin{array}{llll}\text { A) } 185 \mathrm{~J} & \text { B) } 433 \mathrm{~J} & \text { C) } 575 \mathrm{~J} & \text { (D) } 720 \mathrm{~J}\end{array} \)

Deux charges ponctuelles \( \mathrm{q}_{1}=10 \mu \mathrm{C} \) et \( \mathrm{q}_{2}=30 \mu \mathrm{C} \) sont placées respectivement en A et B distantes de 40 cm . 1) Calcule le module du champ électrique \( \overrightarrow{\mathrm{E}} \) au point M milieu de AB . 2) Détermine le point P de \( [\mathrm{AB}] \) où le champ est nul. 3) Détermine le module du champ électrique \( \overrightarrow{\mathrm{E}} \) a) En un point N situé entre A et B à 10 cm de A . Représente ce champ sur un schéma clair. b) En un point Q situé sur lá médiatrice de AB à 20 cm du milieu M de AB .

A lamp hangs vertically from a cord in a descending elevator that accelerates at \( 2.4 \mathrm{~m} / \mathrm{s}^{2} \). If the tension in the cord is 89 N . The mass of the lamp in \( (\mathrm{kg}) \) is:

Ejemplo 2 Encontremos la velocidad de una bala de 0.02 kg que adquiere una energia cinética de 400 J. \( \begin{array}{lll}\text { Datos: } \\ m=0.02 \mathrm{~kg} & E_{k}=\frac{1}{2} m v^{2} \\ E_{k}=4001 & \frac{2 E_{k}}{m}=v^{2} & \begin{array}{l}\text { Despejamos la velocidad dejándola e } \\ \text { uno de los lados de la ecuación. }\end{array}\end{array} \)

II. Workout the following problems 8. A vertical, solid steel post 25 cm in diameter and 2.50 m long is required to support a load of 8000 kg . You can ignore the weight of the post. What are (a) the stress in the post; (b) the strain in the post; a (c) the change in the post's length when the load is applied?