Test: Motion and Measurement of Distances - Grade 9 MCQ

We decide whether an object is in motion or at rest based on -

• If an object changes its position with time, it is in motion.
• If an object does not change its position with time, it is at rest.

Hence, option C is correct.

The length will be 8.8 cm.
If zero mark is not visible, you can use any other full mark on the scale and then subtract the reading of this mark from the reading at the other end.
10.8 - 2 = 8.8 cm

Stone Motion Analysis:

• Rectilinear Motion: The stone dropped from the roof of a 7-story building will have rectilinear motion. This means that the stone will move along a straight line path as it falls towards the ground.

We know,
1 cm=0.01 m
1 mm=0.001 m
1 km=1000 m
Out of these, 1 mm is the smallest measurement unit of the length. 

When no force acts on a body, it can either be at rest or in uniform motion, according to Newton's First Law of Motion. This law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.
Moving is not necessarily correct on its own because "moving" could imply that the object is accelerating or changing direction, which would require a force to be acting on it.

Complete step-by-step answer:
Given data:
The reading of the ruler at one end = 3.0 cm
And the reading of the ruler at the other end = 33.1 cm
While measuring the length of the knitting needle with a ruler the actual reading of the knitting needle is the difference of the final reading and initial reading.
I.e. the difference of the reading of the ruler at the other end and the reading of the ruler at the one end.
So the actual reading of the knitting needle or the length of the needle = reading of the ruler at the other end – reading of the ruler at one end.
Now substitute the values we have,
So the actual reading of the knitting needle or the length of the needle = 33.1 cm – 3.0 cm = 30.1 cm.
So the length of the needle is 30.1 cm.
So this is the required answer.

• Scientists worldwide use the metre (m) as the standard unit of length for measuring things.
• A metre is a little longer than a yardstick and is divided into smaller units like centimetres and millimetres.
• So, when scientists want to measure how long something is, they use a metre to keep their measurements consistent with others around the world.