Electric field intensity at a point on the a line of an electric dipole.

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 \( (h=0) \) ?

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 T on both weights along the direction of the rope, and the coefficient of friction between the surface and boxes is 0.4 . If the box on the right weighs 100 pounds and the angle of the ramp is \( 36^{\circ} \), 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 (Do not round until the final answer. Then round to two decimal places as needed.)

Un automóvil se desplaza a ựna velocidad de \( 90 \mathrm{~km} / \mathrm{h} \) y para mantener esta velocidad debe vencer a un conjunto. de fuerzas equivalentes a 2400 N . Determina el trabajo realizado por el automóvil en un recorrido de 10 km . a. 2160000 J b. 24000000 J c. 24000 J d. 216000 J

- 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 \( 2 \mathrm{~mm} .\left(\rho_{\text {hielo }}=0,9 \mathrm{gf} / \mathrm{cm}^{3}\right) \).

Answer True or False. 1. In motion means moving. 2. Scientists do not use a frame of reference to talk about motion. 3. You cannot tell whether an object is in motion unless you have frame of reference. 4. A frame of reference is some other object to which you compar an object's position. 5. When scientists study the motion of stars in the sky, they use clouds as a frame of reference.