Un jardinero empuja su podadora de 18 Kg de masa sobre un terreno horizontal mediante una fuerza de 100 N que forma un ángulo bajo la horizontal de \( 30^{\circ} \), si el coeficiente de rozamiento podadora - césped es 0,25 , y parte del reposo, después de 8 segundos ¿Qué potencia desarrolla el jardinero? Respuesta:

(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?

1.10 How much energy in kWh is needed to keep a 60 W light on for 8 hours A 48 kWh B \( 4,8 \mathrm{kWh} \) C \( 0,48 \mathrm{kWh} \) D 480 kWh

28.11. Un alambre largo y recto está a lo largo del eje \( z \) y conduce \( u \) corriente de 4.00 A en la dirección \( +z \). Determine el campo magnétic (magnitud y dirección) producido en los siguientes puntos por un seg mento de 0.500 mm del alambre con centro en el origen: a) \( x=2.00 \mathrm{~m} \), \( \begin{array}{l}y=0, z=0 ; b) x=0, y=2.00 \mathrm{~m}, z=0 \\ 2.00 \mathrm{~m}, z=0 ; d) x=0, y=0, z=2.00 \mathrm{~m} \text {. }\end{array} \)

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

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 \( 28 \mathrm{~m} / \mathrm{s} \) ? \( \begin{array}{llll}\text { A) } 4 \text { times farther } & \text { B) } 3.2 \text { times farther } & \text { C) } 4.8 \text { times farther } & \text { D) } 5.2 \text { times farther } \\ \text { 21. An object is moving in a straight line with constant acceleration. Initially it is traveling at } 16 \mathrm{~m} / \mathrm{s} .\end{array} \) \( \begin{array}{llll}\text { Three seconds later it is traveling at } 10 \mathrm{~m} / \mathrm{s} \text {. How far does it move during this time? } \\ \begin{array}{llll}\text { () } 30 \mathrm{~m} & \text { B) } 39 \mathrm{~m} & \text { C) } 48 \mathrm{~m} & \text { D) } 57 \mathrm{~m}\end{array}\end{array} \).