Vidaara.orgClass 9 · Physics
CodeVID-P9-03-FMW-01
Free Fall, Mass & Weight — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Take $g = 10\ \text{m/s}^2$ unless stated otherwise.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
During free fall the acceleration of an object is:
- A.$0$
- B.$g$
- C.$2g$
- D.$g/2$
2.
The SI unit of mass is the:
- A.newton
- B.kilogram
- C.joule
- D.pascal
3.
Weight is given by:
- A.$W = m/g$
- B.$W = mg$
- C.$W = g/m$
- D.$W = m + g$
4.
An object's weight on the Moon is about ___ of its Earth weight.
- A.$\dfrac{1}{2}$
- B.$\dfrac{1}{6}$
- C.$6$ times
- D.the same
5.
Which is a vector quantity?
- A.mass
- B.weight
- C.time
- D.distance
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Define free fall.
7.
A ball is dropped from rest. Find its speed after $4\ \text{s}$.
8.
State one difference between mass and weight.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
A stone is dropped from a $45\ \text{m}$ tower. Find the time to reach the ground.
10.
An object of mass $8\ \text{kg}$ is on Earth. Find its weight on Earth and on the Moon.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
A ball is thrown vertically upward at $30\ \text{m/s}$. Find (a) the maximum height, (b) time to reach the top, and (c) total time of flight.
Answer Key
Section A — Multiple Choice Questions
- (B) $g$
- (B) kilogram
- (B) $W = mg$
- (B) $\dfrac{1}{6}$
- (B) weight
Section B — Short Answer (2 marks)
- Motion of an object under the influence of gravity alone, with no other force such as air resistance; its acceleration is $g$.
- $v = u + gt = 0 + 10 \times 4 = 40\ \text{m/s}$.
- Mass (kg) is the amount of matter and is constant; weight (N) is the force of gravity and varies with $g$.
Section C — Short Answer (3 marks)
- $h = \dfrac{1}{2} g t^2 \Rightarrow 45 = 5 t^2 \Rightarrow t = 3\ \text{s}$.
- Earth: $W = 8 \times 10 = 80\ \text{N}$; Moon: $\dfrac{80}{6} \approx 13.3\ \text{N}$.
Section D — Long Answer (5 marks)
- At top $v=0$: $h = \dfrac{u^2}{2g} = \dfrac{900}{20} = 45\ \text{m}$. Time up $= \dfrac{u}{g} = 3\ \text{s}$. Total flight $= 2 \times 3 = 6\ \text{s}$.
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