Which part of the electromagnetic spectrum has a wavelength shorter than the color of the visible light spectrum

When you drop a pebble from height a it reaches the ground with speed v if there is no air resistance. from what height should you drop it so it will reach the ground with three times the speed? (a) 9m (b) 3m (c) 6m (d) 18m

Why is it important always to use horizontal bars in unit fractions when performing unit conversions?

If you place a magnet under a clear dish, and sprinkle iron fillings over it, above what part of the magnet will most of the fillings gather