Measurements in Physics (DP IB Physics: SL)

Blue light has a wavelength of 450 nm.

Which of the following also represents this wavelength?

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 60 cm × 60 cm.

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?

The frictional force F on a sphere falling through a fluid is given by the formula:

F =  

In this equation, a is the radius of the sphere, η is a constant relating to the fluid and v is the velocity of the sphere.

What are the units of η?

The speed v of a liquid leaving a tube depends on the change in pressure ΔP and the density ρ of the liquid. The speed is given by the equation:

v = k

In this equation, k is a constant that has no units.

What is the value of n?

Which estimate is realistic?

The theory of gas flow through small diameter tubes at low pressures is an important consideration of high vacuum techniques.

One equation used in this theory is:

Q =

Where k is a unitless constant, r is the radius of the tube, p₁ and p₂ are the pressures at each end of the tube, L is the length of the tube, M is the molar mass of the gas, R is the molar gas constant and T is the thermodynamic temperature of the gas.

What are the base units of Q?

What is the correct value for the Gravitational constant?

A boy jumps from a wall 5 m high. What is an estimate of the change in momentum of the boy when he lands without rebounding?

When a constant braking force is applied to a vehicle moving at speed v, the distance d moved by the vehicle as it comes to rest is given by the expression:

d = kv²

In this equation, k is a constant.

When d is measured in metres and v is measured in metres per second, the constant has a value of k₁.

What is the value of the constant when the distance is measured in metres, and the speed is measured in kilometres per hour?

What is the unit for the gas constant in fundamental SI units?

Which of the following gives the correct unit for ?

The drag coefficient C_d is a number with no units. It is used to compare the drag on different cars at different speeds. It is given by the equation

 C_d = 

F is the drag force on the car, ρ is the density of the air, A is the cross-sectional area of the car and v is the speed of the car.

 What is the value of n?