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.

A mass m is traveling at an initial speed \( v_{i}=25.0 \mathrm{~m} / \mathrm{s} \). it is brought to rest in a di ff 62.5 m by a force of 15.0 N . The mass is:

(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? \( \begin{array}{llll}\text { A) } 185 \mathrm{~J} & \text { B) } 433 \mathrm{~J} & \text { C) } 575 \mathrm{~J} & \text { (D) } 720 \mathrm{~J}\end{array} \)

A \( 20-\mathrm{m} \) long steel wire (cross-section \( 1 \mathrm{~cm}^{2} \), Young's modulus \( 2 \times 10^{11} \mathrm{~N} / \mathrm{m}^{2} \) ), is subjected to a load of \( 25,000 \mathrm{~N} \). How much will the wire stretch under the load? \( \begin{array}{lllll}\text { A) } 0.25 & \text { B) } & 2.5 \mathrm{~cm} & \text { C) } 12.5 \mathrm{~cm} & \text { D) } 25 \mathrm{~cm}\end{array} \) \( \begin{array}{llll} & \text { B) } 1.25 \mathrm{~cm}\end{array} \)

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:

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?