A room measuring 21 m by 18 m and 13 m high has to be lighted by four lighting fixtures suspended 3 m from ceiling. The ceiling points are symmetrically placed on the two diagonals so that each point is 7 m from the center of the ceiling. An illumination of 12 lux apart from any effect due to the walls and ceiling is required on the center of a table 3 m high placed at the center of the room. What luminous intensity must each unit give in direction necessary to produce this result?

You are given a vector a = 125i and an unknown vector b that is perpendicular to a. the cross-product of these two vectors is a × b = 98k. what is the y-component of vector b?

Compare the horizontal displacement of the two balls as they travel to the ground. what do you observe?

An alpha particle with kinetic energy 12.5 mev makes a collision with lead nucleus, but it is not "aimed" at the center of the lead nucleus, and has an initial nonzero angular momentum (with respect to the stationary lead nucleus) of magnitude l = p0 b, where p0 is the magnitude of the initial momentum of the alpha particle and b=1.40×10−12 m. (assume that the lead nucleus remains stationary and that it may be treated as a point charge. the atomic number of lead is 82. the alpha particle is a helium nucleus, with atomic number 2.) what is the distance of closest approach?