Q1. A block of wood has specific gravity 0.80. While placed in water, what percent of the volume of the wood is above surface?

Q2. When a wood shelf of mass 6.20 kg is fastened inside a slot in a vertical support, support exerts a torque on the shelf.

Q3. Galaxies form by gravitational collapse of regions that are denser than average. Noting that the present day average mass density of the universe is ρ = 3 × 10-30 g/cm-3, estimate how long it takes for a galaxy to collapse. Hint: You only require assuming a density for the region before collapse, even though your estimate will be uncertain by a factor of order unity. Does your answer make sense compared to the age of the universe? If there is the conflict, what assumptions might you improve in order to reconcile it?