1.1 Measurements in Physics

The table contains some quantities, together with their symbols and units.

Which expression has the units of energy?

For which quantity is the magnitude a reasonable estimate?

kilowatt-hours (kW h) is equivalent to

The equation of hydrostatic pressure relates the pressure of a fluid, P, to the density of the fluid, ρ

 P = ρgΔh

 where g is the gravitational field strength, and Δh is the depth from the surface of the fluid.

 How can both sides of this equation be written in terms of SI base units?

The units of all physical quantities can be expressed in terms of SI base units.

 Which pair contains quantities with different base units?

The best estimate for the time it takes light to cross the nucleus of a hydrogen atom is:

A glider is momentarily stationary in the air before losing 1.00 m of vertical height for every 6.00 m that it goes forward horizontally. The horizontal speed of the glider is 12 m s^–1.

What is the vertical speed of the glider, to an appropriate number of significant figures, after it falls a total of 31.25 m?

The graph shows the data for the variation of the power output of a photovoltaic cell with load resistance. The data were obtained by placing the cell in sunlight. The intensity of the energy from the Sun incident on the surface of the cell was constant.

The intensity of the Sun’s radiation incident on the cell is 0.6 W m^–2. The active area of the cell has dimensions of 30 mm × 30 mm.

At the peak power, what is the ratio ?

An object falls for a time of 0.081 s. The acceleration of free fall is 9.81 m s^–2. The displacement is calculated. Which of the following gives the correct number of significant digits for the calculated value of the displacement of the object?