As light from a star races through our atmosphere, it bounces and bumps through the different layers, bending the light before you see it. Since the hot and cold layers of air keep moving, the bending of the light changes too, which causes the star's appearance to wobble or twinkle.
S.G. or specific gravity is the ratio of the density of an object to a fluid. It also is the fraction of the object's volume that would be submerged if the object were placed in the fluid. (note: if S.G.>1, the object will sink)
S.G. = density(wood) / density(water)
2/3 = density(wood) / 1000
density(wood) = 2000/3 kg/m^3 = ~666.67 kg/m^3
S.G. = density(wood) / density(oil)
9/10 = 2000/3 / density(oil)
density(oil) = 2000/3 / 9/10 = 20000/27 kg/m^3 = ~740.74 kg/m^3
Acceleration is equal to the change in velocity per unit time. In this case, velocity has changed from 17.7 m/s to 14.1 m/s, which is a decrease of 3.6 m/s. This takes place in 12 seconds, so the average acceleration is 3.6 m/s / 12s = 0.3 m/s^2. The direction of this acceleration is south, since the car's northbound speed is decreasing.
Use Coulomb law: F = k * q1*q2 / (r^2), where k = 9.00 * 10^9 N.m^2/C^2
F = 9.00 * 10^9 N.m^2/C^2 * 2.4*10^-8 C * 1.8*10^-6 C / [0.008m]^2 = 38.88 * 10^ -5 N
F = 39 * 10 -5N
