9. Motion and Time

Solve the following questions:

Q1. A bus covers a distance of 480 km in 8 hours. What is its speed?

Ans:

Distance travelled = 480km

Time taken = 8h

Speed = distance / time

  = 480 / 8 = 60 km/h

The speed of the bus is 60km/h.

Q2. A pendulum completes 50 oscillations in 120 seconds. What is its time period? 

Ans:

Total Number of oscillations = 50

Time for taken for 50 oscillations = 120s

Time period = Time taken / total oscillations

  = 120 / 50 = 2.4s

Time period of the pendulum is 2.4 seconds.

Q3. Speed of a car is 70 km /h. Find the distance travelled by car in 45 minutes.

Ans:

Speed = 70km/h

Time = 45 min = 45/60 = 0.75 hours

(**As the time is in minutes & speed is in km/h we need to convert unit of time to hours)

Distance = Speed x time

     = 70 x 0.75 = 52.5 km

Distance travelled by the car is 52.5km.

Q4. A van covered a distance of 60 km in 25 minutes. Find the speed in m/s.

Ans:

As we require speed in m/s, lets convert the give units in appropriate unit.

Distance = 60km = 60 x 1000 = 60000m

Time = 25 min = 25 x 60 = 1500 sec

Speed = Distance / Time

  = 60000 / 1500 = 40 m/s

The speed of the van is 40 m/s.

Q5. A vehicle travels from 3570 km to 3690 km from 9.30 to 11.00 am. What is the speed of the vehicle?

Ans:

Distance travelled = 3690 - 3570 = 120 km

Time taken = 11.00 - 9.30 = 1.5 hours

Speed = Distance / Time

  = 120 / 1.5 = 80 km/h

The speed of the vehicle is 80 km/hr.

Answer the following in short:

Q1. What is motion?

Ans:

Motion is the change in position of an object within given time.

Q2. What are the different types of motion?

Ans:

The different types of motion are straight line, circular & periodic (oscillatory).

Q3. Define speed & state its formula.

Ans:

Speed is the distance covered by an object in a unit time.

Speed = Distance / Time

Q4. State the different units to measure speed.

Ans:

The different units to measure speed are: meter per second (m/s), meter per minute (m/min) & kilometer per hour (km/h).

Q5. What is a simple pendulum & its type of motion?

Ans:

A simple pendulum consists of a small metallic ball called the bob suspended by a thread or string from a rigid stand such that the bob can swing to & fro freely.

The motion of a simple pendulum is a periodic or oscillatory motion.

Q6. How time was measured in ancient time?

Ans:

Time was measured using sundials, water & sand clocks during ancient time.

Q7. What does a straight line on a distance-time graph indicate?

Ans:

A straight line indicates that an object is moving at a constant speed. The steeper the line, the faster is the speed.

Q8. What is a periodic motion?

Ans:

A motion that repeats after equal interval of time is called periodic motion.

Examples: motion of a swing, to & fro motion of pendulum.

Q9. How will the distance time graph be for a body at rest?

Ans:

The distance time graph will be a straight line parallel to the x axis for a body at rest.

Q10. What is the time period of a pendulum?

Ans:

Time period is the time taken by the pendulum to complete one oscillation.

Answer the following question:

Q1. Differentiate between uniform & non-uniform motion.

Ans:

Q2. What time of clocks are used today? state its benefits.

Ans:

1. The clocks or watches used today have an electric circuit with one or more cells.
2. These clocks are called quartz clocks.
3. The time measured by quartz clocks is much more accurate than the clocks available earlier.

Q3. How to choose a scale for the distance time graph?

Ans:

A distance time graph is a graphical representation showing the relationship between distance traveled and time taken by an object.

To choose the correct scale we need to consider the following points:

1. The difference between the highest and the lowest values of distance & time.
2. The intermediate values of each quantity, so that with the scale chosen it is convenient to mark all the values on the graph.
3. The scale should be able to utilize the maximum part of the graph paper on which the graph is to be drawn.