What type of motion is observed in the substance during the time duration of 0 to 4 hours of science paper ​

The boy of mass 30 kg is at r1= 2 meters from the fulcrum. of the girl is 45 kg, at what r2 must she sit so that they are balanced ?

Light traveling in water, nwater = 1.33, strikes a plastic block at an angle of incidence of 51.4°; part of the beam is reflected and part is refracted. if the index of refraction of the plastic is 2.0, what is the angle made by the reflected and refracted beams?

Give an example in which the electrical energy changes to light energy