CBSE Class 7 Science Advanced Physics Kinematics Very Short Answer Questions Set 01

Very Short Answer Questions

Question 1. Two hour is equal to ________ seconds.
Answer:
7200 seconds.
1 hour = 60 minutes = 3600 s, so 2 hours = 2 × 3600 = 7200 s.
In simple words: Two hours contain 7200 seconds.

Teacher's Note:
1. Multiply the hours by 3600 to get seconds.
2. Learn 1 h = 3600 s as a standard conversion.

Question 2. The motion of molecules in a solid is an example for ________ motion.
Answer:
Vibratory motion.
The molecules of a solid are held in fixed positions and only move to and fro very quickly about their mean positions.
In simple words: Molecules in a solid shake very fast about fixed places, which is vibratory motion.

Teacher's Note:
1. Vibratory motion is a fast to-and-fro motion.
2. Guitar strings and drum membranes are other examples.

Question 3. One millisecond is ________ part of a second.
Answer:
\( \frac{1}{1000} \) part of a second.
Milli means one thousandth.
In simple words: A millisecond is one-thousandth of a second.

Teacher's Note:
1. The prefix milli always means 1/1000.
2. Similarly, one microsecond is one-millionth of a second.

Question 4. A body moving with a velocity of 10 m s⁻¹ increases its velocity to 20 m s⁻¹ in 2 s. Then the rate of change in velocity is ______.
Answer:
Rate of change of velocity = acceleration = \( \frac{v - u}{t} = \frac{20 - 10}{2} \) = 5 m s⁻².
In simple words: The velocity grows by 5 m s⁻¹ every second.

Teacher's Note:
1. Rate of change of velocity is the acceleration.
2. The unit of the answer is m s⁻².

Question 5. A car moves with a constant velocity, its average velocity is equal to its ______.
Answer:
Its velocity (the constant velocity itself).
When the velocity does not change, the average of the velocity is the same value at all times.
In simple words: With no change in velocity, the average velocity is the same constant velocity.

Teacher's Note:
1. Constant velocity means both speed and direction stay the same.
2. Average velocity = total displacement ÷ total time gives the same value.

Question 6. The time period of a simple pendulum depends on its ________.
Answer:
Length.
T = 2π√(ℓ/g), so for a given place the time period depends only on the length of the pendulum.
In simple words: Only a longer or shorter string changes how long one swing takes.

Teacher's Note:
1. It does not depend on the mass, size or shape of the bob.
2. T is proportional to the square root of the length.

Question 7. A body moves with uniform speed of u m s⁻¹ towards east, then the body is said to possess ________ velocity.
Answer:
Uniform velocity.
Both the speed (u) and the direction (east) remain the same.
In simple words: Same speed and same direction means uniform velocity.

Teacher's Note:
1. Uniform velocity needs both magnitude and direction to be constant.
2. If the direction changes, the velocity becomes variable even when the speed is constant.

Question 8. The time taken by the bob of a simple pendulum of time period (T) to move from one extreme position to the other extreme position is equal to ________.
Answer:
\( \frac{T}{2} \).
One oscillation means going from one extreme to the other and back again, so going from one extreme to the other is half an oscillation.
In simple words: Going only one way across takes half of the time period.

Teacher's Note:
1. One oscillation = extreme to extreme and back.
2. So T/2 is the time for a single crossing.

Question 9. ________ measures the distance moved by a vehicle.
Answer:
Odometer.
A speedometer, in contrast, records the speed.
In simple words: An odometer counts the kilometres a vehicle has travelled.

Teacher's Note:
1. The odometer reading difference gives the distance covered.
2. Speedometer and odometer are both fitted on the dashboard.

Question 10. A body is said to be moving with uniform speed if it covers equal distances in ________.
Answer:
Equal intervals of time.
This must hold however small the time interval is.
In simple words: Equal distance in each equal time means uniform speed.

Teacher's Note:
1. Remember both words 'equal': equal distances and equal intervals.
2. Even a small interval of time must give the same distance for the speed to be uniform.

Question 11. One microsecond is ________ of a second.
Answer:
\( \frac{1}{10^{6}} \) (one millionth) of a second.
In simple words: A microsecond is one millionth of a second.

Teacher's Note:
1. Micro means one millionth, that is, 10⁻⁶.
2. A nanosecond is 10⁻⁹ s.

Question 12. SI unit of speed is ________.
Answer:
m s⁻¹ (metre per second).
In simple words: Speed in SI is measured in metres covered each second.

Teacher's Note:
1. Speed = distance ÷ time, so the unit is a distance unit over a time unit.
2. km h⁻¹ is the unit usually used for vehicles.

Question 13. One kilometre is equal to ________ metre.
Answer:
1000 metre.
In simple words: Kilo means one thousand, so 1 km is 1000 m.

Teacher's Note:
1. Kilo = 1000.
2. Use this to convert km h⁻¹ into m s⁻¹ along with 1 h = 3600 s.

Question 14. The time taken by the pendulum to complete one oscillation is called ________.
Answer:
Time period.
In simple words: The time for one full to-and-fro swing is the time period.

Teacher's Note:
1. Its symbol is T and its SI unit is the second.
2. Frequency is the reciprocal of the time period.

Question 15. The distance covered by an object in a unit time is known as the ________ of the object.
Answer:
Speed.
In simple words: Distance covered each second is the speed.

Teacher's Note:
1. Speed = distance ÷ time.
2. The unit time may be a second, a minute or an hour.

Question 16. An object moving along a straight line with a constant speed is said to be in ________.
Answer:
Uniform motion.
In simple words: Straight-line motion at steady speed is uniform motion.

Teacher's Note:
1. Its distance-time graph is a straight sloping line.
2. A body in uniform motion has zero acceleration.

Question 17. The speed of the bob of a simple pendulum is maximum at its ________.
Answer:
Mean position.
The bob slows down as it goes towards an extreme position and stops for a moment there, so it moves fastest at the mean position.
In simple words: The bob is quickest in the middle and slowest at the ends.

Teacher's Note:
1. At the extreme positions the speed is zero.
2. The mean position is the rest position of the bob.

Question 18. The time period of a simple pendulum of length 1 m is ________ second. (Take π² = 10, g = 10 m s⁻²)
Answer:
T = 2π√(ℓ/g) = 2π√(1/10).
T² = 4π² × \( \frac{1}{10} \) = 4 × 10 × \( \frac{1}{10} \) = 4, so T = 2 s.
In simple words: A pendulum 1 m long takes about 2 s for one swing.

Teacher's Note:
1. Square both sides to avoid carrying a square root of π.
2. A 1 m pendulum is roughly a seconds pendulum.