Time and Motion
Q: How do we determine the speed of a moving object?
A: Vehicles such as cars, buses, scooters and bikes have devices that measure the speed of the vehicle and the distance covered by it. Speed of the vehicle is measured by a device called the speedometer. The speedometer shows the speed of vehicle in km/h. Inside the speedometer, there is an instrument called odometer. The odometer records the distance covered by the vehicle in kilometers.
Q: List any 4 types of watches used today.
A: Analog clock, Digital clock, Stopwatch, Smartwatch.
Q: What is the working principle of an hourglass?
A: Worked on the principle that a definite quantity of sand takes the same time to fall from the upper chamber to lower chamber.
Q: How do we change the time period of simple pendulum?
A: By changing the length of the pendulum.
Q: What is the principle of a water clock?
A: A water clock also known as clepsydra is also used to measure time. It works on the principle that equal amounts of water take the same interval of time to flow through an opening. Early water clocks existed as early as 1600 BC but they were not very accurate.
Q: What is the difference between uniform and non uniform motion?
A: A body moving in a straight line covering equal distance in equal intervals of time is said to be moving in uniform motion (e.g., a car covers a distance of 50 meters every 10 sec). A body moving in a straight line covering unequal distance in equal intervals of time or equal distances in unequal intervals of time is said to be moving in non-uniform motion (e.g., a car covering 50 meters, 90 meters, 130 meters and 230 meters every 10 sec).
Q: What factors do we consider to conclude whether an object is moving fast or slow?
A: The motion of an object with respect to another object depends upon the following factors: 1. The distance covered by the object. 2. The time taken to cover the distance. Therefore, we can conclude: 1. A body that covers a given distance in less time is said to move faster and the one which takes a long time to cover the same distance is said to move slower. 2. A body which covers more distance in given intervals of time is said to move faster than the one which covers less distance in same interval of time.
Q: Define the following terms:
i) Time:
A: Time is defined as the period between two events.
ii) Oscillation:
A: When the bob of the pendulum is at point (mean position) it is said to be in its mean position. When the bob of the pendulum is displaced slightly and released, it begins to move back and forth. The back and forth motion of a simple pendulum is called oscillation.
Math / Physics Word Problems
Q: In the Olympic game an athlete ran 3.5 km in 14 minutes. Her average speed was __ m/s during the race.
A: Total distance covered = 3500 m. Total time taken = 840 s. Speed = 3500 / 840 m/s.
Q: A migrating bird can travel at a speed of 30 m/s. The bird will travel __ km in 25 min at this speed.
A: Speed = 30 m/s, Total time taken = 1500 s. Total distance covered = 30 * 1500 = 45000 m = 45 km.
Q: A cargo ship travel at a speed of 10 m/s. It will take __ hr to travel between two ports that are 600 km apart.
A: Total distance covered = 600000 m, Speed = 10 m/s. Total time taken = 600000 / 10 = 60000 s = 16.67 hrs.
Q: A car covers 67 km in first hr, 73 km in the next hr. Find its average speed.
A: Total distance covered = 67 + 73 = 140 km. Total time taken = 1 + 1 = 2 hr. Average speed = 140 / 2 = 70 km/h.
Q: Calculate speed and identify type of motion for a car travelling 12 km in 30 min, 17 km in 30 min, and 8 km in 30 min.
A: Total distance covered = 12 + 17 + 8 = 37 km. Total time taken = 30 + 30 + 30 = 90 min (1.5 hr). Speed = 37 / 1.5 = 24.67 km/hr. The car covers unequal distances in equal intervals of time, hence it moves in non-uniform motion.