Item 21. Uma bola é largada do alto de um edificio e cai em direção ao solo. Sua altura \( h \) em relação ao solo, \( t \) segundos após o lançamento, é dada pela expressăo \( h=-20 t^{2}+ \) 3380. Após quantos segundos do lançamento, a bola atingirá o solo \( (h=0) \) ?

1. If you were to visit a planet that was much more massive than earth, your mass would be a) More b) Less c) The same d) Impossible to tell without knowing which planet you are visiting. 2. Which of the following is not a form of light? a) radio waves b) microwaves c) x-rays d) All of the above are a form of light. e) None of the above is a form of light

- Cuál es el área mínima de un bloque de hielo flatando en el ugua para poder sustentar a un aulomóvil que pesa 1200 kg f?. El bloque tiene una altura de \( 2 \mathrm{~mm} .\left(\rho_{\text {hielo }}=0,9 \mathrm{gf} / \mathrm{cm}^{3}\right) \).

Una esfea de Jan esta unifarmanate cargada con una densidad de carga de \( \frac{1.2 \times 10^{-5}}{\pi} \frac{\mathrm{c}}{\mathrm{m}^{3}} \). Calcular el modo del campo electrico a una distancia centro, en el interior \( (r<5) \) y en el exterior \( (r>5) \).

1. A ciarge of \( 2 \mu \mathrm{C} \) is placed 0.1 m away from another charge of \( -3 \mu \mathrm{C} \). Using Coulomb's law. calculate the force between them. (Assume \( \left.k=8.99 \times 10^{9} \mathrm{~N} \mathrm{~m}^{2} / \mathrm{C}^{2}\right)(5 \mathrm{Marks} \) ) Calculate the electric field at a point where a \( 5 \mu \mathrm{C} \) charge experiences a force of 0.2 N . ( 5 Marks) An 1 C voltage of \( V(t)=220 \sin (100 \pi t) \) is applied to a \( 50 \Omega \) resistor. Calculate the pecie current through the resistor. ( 5 Marks) A capacitor with a capacitance of \( 20 \mu \mathrm{~F} \) is connected in an AC circuit with a frequency of 50 Hz . Calculate the capacitive reactance. ( 5 Marks )

A box sitting on a horizontal surface is attached to a second box sitting on an inclined ramp by a rope that passes over an ideal pulley. The rope exerts a tension force I on both weights along the direction of the rope, and the coefficient of friction between the surface and boxes is 0.6 . If the box on the right weighs 100 pounds and the angle of the ramp is \( 35^{\circ} \), how much must the box on the left weigh for the system to be in static equilibrium? The box on the left must weigh approximately \( \square \) pounds for the system to be in static equilibrium. (Do not round until the final answer. Then round to two decimal places as needed.)