All questions of How Fast? for Grade 9 Exam

• The speedometer is a device found in vehicles that measures the current speed of the vehicle.
• It provides real-time information, allowing drivers to maintain safe speeds and abide by traffic regulations.
• Unlike an odometer, which measures distance traveled, the speedometer focuses solely on speed.
• Ammeter and voltmeter measure electrical current and voltage, respectively, and are not related to vehicle speed.

When the slope of distance-time graph is a straight line parallel to time axis, the object is moving with uniform motion.

Speed in km/min
=15 km/20 min
=0.75 km/min
In km/h,
0.75×60 = 45 km/h

Understanding the Problem
To find the time period of a simple pendulum, we need to understand the relationship between the number of oscillations and the total time taken for those oscillations.

Given Data
- Total oscillations = 20
- Total time = 32 seconds

Calculating Time Period
The time period (T) of a pendulum is defined as the time it takes to complete one full oscillation. We can calculate it using the formula:

• Time Period (T) = Total Time / Number of Oscillations

Now, substituting the given values into the formula:

• T = 32 seconds / 20 oscillations
• T = 1.6 seconds

Conclusion
Thus, the time period of the pendulum is 1.6 seconds. Therefore, the correct answer is option 'A'.

Key Takeaways
- The time period indicates how long it takes for one complete oscillation.
- This calculation is essential in understanding the dynamics of pendulums, which are a fundamental concept in physics.
With this understanding, you can confidently solve similar problems involving simple harmonic motion and pendulums!

Oscillatory motion involves an object moving to and fro about a fixed point, such as the motion of a pendulum or the hands while running.

Non-uniform Motion:

Movement of an asteroid, a car coming to a halt, and a bouncing ball are all examples of non-uniform motion. Non-uniform motion refers to an object moving at varying speeds or changing its direction over time.

Movement of an Asteroid:
- An asteroid moving through space does not maintain a constant speed as it is influenced by gravitational forces from other celestial bodies. It may speed up or slow down as it travels through the solar system.

A Car Coming to a Halt:
- When a car is slowing down to come to a stop, it is experiencing non-uniform motion. Initially, the car is moving at a certain speed, but as the brakes are applied, the speed decreases until it eventually comes to a complete stop.

A Bouncing Ball:
- A bouncing ball is another example of non-uniform motion. When a ball is thrown or dropped, it accelerates towards the ground due to gravity. Upon hitting the ground, it bounces back up, changing its speed and direction multiple times during the bouncing process.

Conclusion:
- All three examples exhibit non-uniform motion because they involve changes in speed or direction over time. Understanding non-uniform motion is essential in physics as it helps to describe the motion of objects in real-world scenarios.

Explanation:
The correct answer is option 'A' - Time of the first bell in the school.

Time intervals:
Time intervals refer to a specific duration or period of time. They measure the amount of time between two points or events.

Options:

a) Time of the first bell in the school:
This option does not express a time interval. It refers to a specific point in time when the first bell rings in the school. It does not indicate a duration or a period of time. Therefore, it is not an example of a time interval.

b) A day:
A day represents a time interval. It refers to a period of 24 hours, starting from midnight and ending at the next midnight. It is a commonly used unit of time to measure the duration of various activities or events.

c) A second:
A second is another example of a time interval. It is a unit of time measurement in the International System of Units (SI). It represents a duration of 1/60th of a minute or 1/3,600th of an hour. It is commonly used to measure short durations or intervals.

d) A school period:
A school period is also a time interval. It refers to a specific duration of time allocated for a particular subject or activity in a school. It can vary in length depending on the school's schedule and may range from a few minutes to an hour.

Conclusion:
Out of the given options, the only one that does not express a time interval is option 'A' - Time of the first bell in the school. This option refers to a specific point in time rather than a duration or period of time.