Formative Practice 2.8 – Physics Form 4 Chapter 2 (Force and Motion I)

Question 1:
What is the meaning of gravitational field strength?

Answer:
Gravitational field strength, g is the force acting per unit mass caused by gravitational pull or as the ratio of the weight to mass of the object.

For objects on the surface of the Earth, gravitational field strength, g is 9.81 N kg^–1. Each 1 kg mass experiences a force of gravity of 9.81 N.

$$\text { Gravitational field strength, } g=\frac{W}{m} \quad\left(\text { Unit }=\mathrm{N} \mathrm{~kg}^{-1}\right)$$

Question 2:
State the differences between mass and weight.

Answer:

Question 3:
A 10 kg object has a weight of 150 N on a planet.
(a) What is the gravitational field strength on the planet?
(b) Is the planet bigger than Earth? Give reasons for your answer.

Answer:
(a)
$$\begin{aligned} W & =m g \\ 150 & =10 g \\ g & =\frac{150}{10} \\ & =15 \mathrm{~N} \mathrm{~kg}^{-1} \end{aligned}$$

(b)
Yes, the planet bigger than Earth.
Gravity of planet 15 N kg^-1 > Gravity of the earth 9.81 N kg^-1

Question 4:
An astronaut of mass 60 kg is assigned to explore the Moon. What is the astronaut’s weight on the Moon’s surface?

Answer:
$$\begin{aligned} W & =m g \\ W_{\text {earth }} & =60 \times 9.81 \\ & =588.6 \mathrm{~N} \end{aligned}$$
Gravitational field strength on the Moon is 1/6 of the gravitational field strength on Earth.
$$\begin{aligned} W_{\text {moon }} & =\frac{1}{6} \times 588.6 \\ & =98.1 \mathrm{~N} \end{aligned}$$