It takes the elevator in a skyscraper 4.5s to reach its cruising speed of 11m/s . a 70kg passenger gets aboard on the ground floor.
a- what is the passenger's weight before the elevator starts moving?
b-what is the passenger's weight while the elevator is speeding up?
c-what is the passenger's weight after the elevator reaches its cruising speed?

A and C are very simple. Since there is no acceleration in both cases, the weight of the passenger is just  (about 690 N or 150 lbs with correct sig-figs). For B, we must first find the acceleration of the elevator. Since , we can write that . Solving for a, we get that . Plugging this into Newton's second law, we get that . When calculating the apparent weight, this gets added onto the 686 N from A and C, so the final apparent weight is about 857 N, or 860 N with the correct number of sig-figs.

tl;dr:
A - 690 N
B - 860 N
C - 690 N

The masses of the objects and their densities

Aform of energy that is reflected or emitted from objects in the form of electrical and magnetic waves that can travel through space. there are many forms of  electromagnetic  energy including gamma rays, x rays, ultraviolet radiation, visible light, infrared radiation, microwaves and radio waves.