Solutions: Motion and Time – Grade VII

Below are the solved questions from the Motion and Time assignment. Each answer is presented in detail for better understanding.

Q1. Answer Briefly

a. The distance-time graph of an object is a horizontal line parallel to the time axis when the object is at rest.

Answer: When the object is at rest.

b. An instrument that indicates the speed of the vehicle is a speedometer.

Answer: Speedometer.

c. Two important devices used in ancient times to measure time are the sundial and the water clock.

Answer: Sundial and water clock.

d. The maximum displacement of the bob from its mean position is called amplitude.

Answer: Amplitude.

e. The clock used for accurate measurement of time is an atomic clock.

Answer: Atomic clock.

f. The speed of a moving object determined to 0.06 m/s is equal to:

Answer: 0.216 km/h.

g. Types of motion represented:

• The tuning fork: Vibratory motion.
• A stone thrown up in the air: Projectile motion.
• A train moving at various speed limits: Non-uniform motion.
• A bullet shot from a pistol: Linear motion.

Q2. Answer the Following Questions

a. A car is running at a speed of 60 km/h. How much time will it take to cover a distance of 27 km?

Answer: 27 minutes.

b. Differentiate between uniform and non-uniform motion with the help of a graph:

Answer: Uniform motion has a straight-line distance-time graph, while non-uniform motion has a curved or irregular graph.

c. Reema observes that her wall clock’s pendulum completes 15 oscillations in 30 seconds:

• i. Answer: A pendulum is a body suspended from a fixed point that swings back and forth under the influence of gravity.
• ii. Answer: 2 seconds.

d. A bus starts from rest at 2:00 PM. The distances covered at various intervals are recorded as follows:

i. Draw a distance-time graph using the data provided (graph can be drawn and added as an image).

ii. Answer: The graph shows uniform motion since the distance increases at a constant rate with time.

e. Sonia’s journey to Shalu’s birthday party:

• Speed for the second part: 12 km/h.
• Average speed for the entire journey: 9 km/h.

f. A car moves with a speed of 40 km/h for 15 minutes and then 60 km/h for the next 15 minutes:

Answer: 25 km.

g. Comment on the working of a sundial:

Answer: A sundial uses the position of the shadow cast by the sun to measure time. It was an ancient device requiring clear sunlight to function effectively.