4) Sanjay shoots a hockey puck in the last 15 seconds of a hockey game. The puck is now sliding toward the goal at 15 meters per second. If its velocity remains constant how much time will it take the puck to slide 27 meters?

(31) Se observa caer de un árbol, una hoja de \( 0,3 \mathrm{~g} \) de masa y a \( 2,3 \mathrm{~m} \) de altura del piso su movimiento es con velocidad constante. Si las fuerzas que actúan sobre la hoja son la fuerza de gravedad y la fuerza de fricción con el aire: a. ¿cuánto trabajo realiza la fuerza de gravedad? b. ¿cuál es la energía cedida al medio por la fric- ción?

20. Assuming equal rates of uniform acceleration in both cases, how much further would you travel if braking from \( 56 \mathrm{~m} / \mathrm{s} \) to rest than from \( 28 \mathrm{~m} / \mathrm{s} \) ? \( \begin{array}{llll}\text { A) } 4 \text { times farther } & \text { B) } 3.2 \text { times farther } & \text { C) } 4.8 \text { times farther } & \text { D) } 5.2 \text { times farther } \\ \text { 21. An object is moving in a straight line with constant acceleration. Initially it is traveling at } 16 \mathrm{~m} / \mathrm{s} .\end{array} \) \( \begin{array}{llll}\text { Three seconds later it is traveling at } 10 \mathrm{~m} / \mathrm{s} \text {. How far does it move during this time? } \\ \begin{array}{llll}\text { () } 30 \mathrm{~m} & \text { B) } 39 \mathrm{~m} & \text { C) } 48 \mathrm{~m} & \text { D) } 57 \mathrm{~m}\end{array}\end{array} \).

ORA PROVA TU Un motoscafo offshore si ferma in \( 10,0 \mathrm{~s} \), frenando con accelerazione costante. In questo intervallo di tempo, percorre 140 m . - Calcola laccelerazione del motoscafo. Determina la sua velocità iniziale in \( \mathrm{km} / \mathrm{h} \). \( \left[-2,80 \mathrm{~m} / \mathrm{s}^{2} ; 101 \mathrm{~km} / \mathrm{h}\right] \)

(b.) student : (1) My Day 9. An airplane starts from rest and accelerates at a constant rate of \( 3.00 \mathrm{~m} / \mathrm{s}^{2} \) for 30.0 s before leaving the ground. a. How far did it move? b. How fast was it going when it took off? 10. A brick is dropped from a high scaffold. a. What is its velocity after 4.0 s ? b. How far does the brick fall during this time? 11. A tennis ball is thrown straight up with an initial speed of \( 22.5 \mathrm{~m} / \mathrm{s} \). It is caught at the same distance above the ground. a. How high does the ball rise? b. How long does the ball remain in the air?

22. An object is moving with constant non-zero acceleration in the \( +x \) direction. The position versus time graph of this object is \( \begin{array}{ll}\text { A) a horizontal straight line. } & \text { B) a vertical straight line. } \\ \text { C) a straight line making an angle with the time axis. } & \text { D) a parabolic curve. } \\ \text { 23. An object is moving with constant non-zero acceleration in the }+x \text { direction. The velocity versus } \\ \text { time graph of this object is } & \text { B) a vertical straight line. } \\ \begin{array}{ll}\text { A) a horizontal straight line. } & \text { D) a parabolic curve. }\end{array}\end{array} \).