Sir Isaac Newton was an English mathematician and physicist - Leaving Cert Physics - Question 6 - 2020

Using Newton's second law of motion, we can find the acceleration by dividing the net force by the mass of the object:

$a = \frac{F_{net}}{m} = \frac{3 ext{ N}}{9 ext{ kg}} = 0.33 ext{ m s}^{-2}$

Newton's third law of motion states that for every action, there is an equal and opposite reaction.

When a rocket takes off, it expels gas downwards at high speed. According to Newton's third law, this action (the downward force of gas) creates an equal and opposite reaction, pushing the rocket upwards. A labelled diagram can illustrate this by showing the rocket and the direction of the gas being expelled.

The kinetic energy (KE) of an object can be calculated using the formula:

$KE = \frac{1}{2}mv^{2}$

Substituting the known values:

$KE = \frac{1}{2} \times 700 ext{ kg} \times (18 ext{ m s}^{-1})^{2} = 113400 ext{ J}$

The acceleration (a) can be calculated using the formula:

$a = \frac{\Delta v}{t} = \frac{18 ext{ m s}^{-1} - 0 }{6 ext{ s}} = 3 ext{ m s}^{-2}$

Using Newton's second law:

$F_{net} = ma = 700 ext{ kg} \times 3 ext{ m s}^{-2} = 2100 ext{ N}$

The net force acts in conjunction with the driving force provided by the engine.

To find the friction force, we can use:

$F_{friction} = F_{driving} - F_{net} = 3000 ext{ N} - 2100 ext{ N} = 900 ext{ N}$

One method of reducing friction is to use lubricants such as oil or grease on the contact surfaces.