Space, time and motion practice questions.

Which of these is an SI base unit?

• the newton (N)
• kilogram
• joule
• watt

Answer: kilogram

The seven SI base units are kg, m, s, A, K, mol and cd. The newton, joule and watt are derived units.

Which of the following is a vector quantity?

• speed
• mass
• velocity
• temperature

Answer: velocity

Vectors have magnitude and direction. Velocity, force, acceleration and momentum are vectors; speed, mass and temperature are scalars.

Newton's first law states that an object continues at constant velocity unless acted on by...

• gravity
• a resultant (net) force
• friction only
• its own inertia or built-in momentum

Answer: a resultant (net) force

The first law (inertia) requires a NET/resultant force to change velocity. Balanced forces give zero acceleration.

A Sankey diagram is used to show...

• the direction and the strength of a magnetic field
• energy transfers and where energy is wasted
• the orbit of a planet
• the structure of an atom

Answer: energy transfers and where energy is wasted

A Sankey diagram shows energy flow: arrow width is proportional to energy. Useful output continues; wasted energy (usually heat) branches off.

For an object in uniform circular motion, the net force is directed...

• along the direction of motion (tangential)
• toward the centre of the circle
• away from the centre of the circle
• vertically downward

Answer: toward the centre of the circle

The centripetal force points toward the centre, causing the direction of velocity to change while speed stays constant.

A ball is thrown vertically upwards. Air resistance is NOT negligible. Compared with the time taken to rise to the maximum height, the time taken to fall back to the starting point is

• shorter
• the same
• longer
• dependent on the mass of the ball

Answer: longer

On the way down the net force (weight minus drag) is smaller than on the way up (weight plus drag), so the downward average acceleration is smaller and the fall takes longer.