what will be the focal lenght of a combined lens made by contact of two lenses of power +3D and -2D.​

Clothes dryer uses about 7 amps of current from a 240 volt line. how much power does it use?

You are driving directly behind a pickup truck, going at the same speed as the truck. a crate falls from the bed of the truck to the road. (a) will your car hit the crate before the crate hits the road if you neither brake nor swerve? (b) during the fall, is the horizontal speed of the crate more than, less than, or the same as that of the truck?

Sound is a disturbance that travels through a medium as a