A 500 kg crate is lifted by a crane and accelerated upward at 2 m/s/s. What is the tension force in the cable pulling up on the crate?

Consider a system to be two train cars traveling toward each other. what is the total momentum of the system before the train cars collide?   kg • what must the total momentum of the system be after the train cars collide?   kg •  

The magnitude of the poynting vector of a planar electromagnetic wave has an average value of 0.939 w/m^2 . the wave is incident upon a rectangular area, 1.5 m by 2.0 m, at right angles. how much total electromagnetic energy falls on the area during 1.0 minute?

Scientific models are based on current knowledge, which can limit their effectiveness when new discoveries are made.