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Q1. Which of the following is a vector quantity?
Velocity is a vector quantity because it has both magnitude and direction. Speed, time, and distance are scalar quantities as they only have magnitude and no direction.
Q2. A train reaches 40 km/h in 10 minutes. Its acceleration is:
Acceleration = change in velocity / time. First part: 40 km/h in 10 min = 4 km/h/min. Converting to m/s²: 40 km/h = 11.11 m/s, 10 min = 600 s, so a = 11.11/600 = 0.0185 m/s². Also, 40 km/h in 10/60 h gives 240 km/h². So both B and C are correct.
Q3. The slope of a distance-time graph gives:
The slope of a distance-time graph is calculated as change in distance divided by change in time, which is the definition of speed. It does not give velocity because direction is not considered.
Q4. Acceleration is positive when it acts:
Acceleration is positive when it acts in the same direction as the velocity of the object. This causes the speed of the object to increase. When acceleration acts opposite to velocity, it is negative (retardation).
Q5. The formula a = (v − u)/t gives:
The formula a = (v – u)/t gives acceleration when it is uniform (constant). It calculates the rate of change of velocity over time. For non-uniform acceleration, this formula cannot be used directly.
Q6. The rate of change of displacement is called:
Velocity is defined as the rate of change of displacement with respect to time. Speed is the rate of change of distance, while acceleration is the rate of change of velocity.
Q7. If an odometer reading changes from 2000 km to 2400 km in 8 h, the average speed is:
Distance traveled = 2400 – 2000 = 400 km. Time = 8 hours. Average speed = distance/time = 400/8 = 50 km/h.
Q8. The equation v = u + at relates:
The equation v = u + at relates velocity and time. It gives the final velocity (v) after time (t) when initial velocity (u) and acceleration (a) are known. It is called the velocity-time relation.
Q9. The symbol ‘u’ represents:
In the equations of motion, the symbol ‘u’ represents the initial velocity of the object at the start of the time interval. ‘v’ represents the final velocity.
Q10. v = (s₂ − s₁)/(t₂ − t₁) gives:
The formula v = (s₂ – s₁)/(t₂ – t₁) gives the average speed or average velocity over a time interval. It calculates the rate of change of position between two points in time.
Q11. Uniform velocity on a distance-time graph means:
When velocity is uniform, the object moves in a straight line without changing direction. In this case, the distance traveled equals the displacement. The distance-time graph would be a straight line, not horizontal (horizontal means at rest).
Q12. Before calculating acceleration, speeds must be converted to:
The SI unit of speed is m/s. Since acceleration is measured in m/s², speeds must be converted to m/s before calculating acceleration. This ensures consistency in units.
Q13. Distance-time graph of an object at rest is:
When an object is at rest, its position does not change with time. So the distance remains constant, and the distance-time graph is a straight horizontal line parallel to the time axis.
Q14. Graphs provide a ______ method to describe motion.
Graphs provide a convenient and visual method to describe and analyze motion. They make it easy to understand relationships between different quantities like distance, velocity, acceleration, and time.
Q15. A speedometer measures:
A speedometer is a device in vehicles that shows the speed at any particular moment. This is called instantaneous speed. It does not measure average speed or velocity.
Q16. When acceleration is opposite to motion, speed:
When acceleration acts in the opposite direction to the motion, it opposes the motion and causes the speed to decrease. This is called retardation or deceleration.
Q17. A body is in non-uniform motion when it:
Non-uniform motion means the object does not cover equal distances in equal intervals of time. Its speed is changing. If it covers equal distances in equal time, it is uniform motion.
Q18. Average velocity is defined as:
Average velocity is the total displacement divided by the total time taken. Displacement is the straight-line distance between the starting and ending points, not the total path length.
Q19. A freely falling body experiences:
A freely falling body experiences uniform acceleration due to gravity (g = 9.8 m/s²). The acceleration is constant throughout the fall (ignoring air resistance), so it is uniform acceleration.
Q20. Example of acceleration opposite to motion is:
When brakes are applied, the acceleration acts in the opposite direction to the motion of the vehicle. This causes the vehicle to slow down. Ball thrown upwards also has acceleration opposite to motion on the way up.
Q21. What does an odometer measure in an automobile?
An odometer is an instrument in a vehicle that records the total distance traveled by the vehicle since it was manufactured or since the last reset.
Q22. If velocity increases equally in equal intervals of time, acceleration is:
When velocity increases by equal amounts in equal intervals of time, the acceleration is constant. This is called uniform acceleration. The rate of change of velocity is the same throughout.
Q23. Which is an example of uniformly accelerated motion?
A freely falling body has uniform acceleration due to gravity (g = 9.8 m/s²). A car moving at constant speed has zero acceleration. Planets have centripetal acceleration which changes direction, and a swing has non-uniform acceleration.
Q24. Why does the sound of thunder reach us later than the lightning flash?
Light travels much faster than sound (3×10⁸ m/s vs 346 m/s). So we see the lightning flash almost instantly, but the sound of thunder takes time to reach us. This is why there is a delay.
Q25. During uniform motion in a straight line:
During uniform motion in a straight line, both speed and direction are constant. Therefore, velocity remains constant. Acceleration is zero because there is no change in velocity.
Q26. The main difference between speed and velocity is that velocity includes:
Speed is a scalar quantity that only has magnitude. Velocity is a vector quantity that includes both magnitude (speed) and direction. This is the primary difference between them.
Q27. Non-uniform acceleration occurs when velocity changes:
Non-uniform acceleration means the acceleration is changing with time. The velocity changes at a rate that is not constant. The velocity-time graph for such motion is curved.
Q28. The change in velocity per unit time is called:
Acceleration is defined as the rate of change of velocity with respect to time. It tells us how quickly the velocity of an object is changing.
Q29. In a distance-time graph, the x-axis represents:
In a distance-time graph, the x-axis (horizontal axis) represents time, and the y-axis (vertical axis) represents distance. The slope of the graph gives speed.
Q30. Uniform velocity means acceleration is:
Uniform velocity means the velocity is constant (both speed and direction are constant). Since there is no change in velocity, the acceleration is zero.
Q31. Uniform acceleration means velocity changes:
Uniform acceleration means the velocity changes by equal amounts in equal intervals of time. The rate of change of velocity is constant throughout the motion.
Q32. The magnitude of average velocity equals average speed when motion is:
Average velocity and average speed are equal only when the motion is along a straight line without changing direction. In this case, the total distance equals the displacement.
Q33. The area under a speed-time graph represents:
The area under a speed-time graph represents the total distance traveled by the object. This is because distance = speed × time, and the area under the curve gives this product.
Q34. A signal takes 5 minutes to travel from a spaceship at the speed of light. What is the distance covered?
Speed of light = 3×10⁸ m/s. Time = 5 minutes = 300 seconds. Distance = speed × time = 3×10⁸ × 300 = 9×10¹⁰ m.
Q35. The formula for acceleration is:
Acceleration is the rate of change of velocity. The formula is a = (v – u)/t, where v is final velocity, u is initial velocity, and t is time taken.
Q36. What is the shape of the path of an object in uniform motion?
Uniform motion means the object moves with constant velocity (both speed and direction constant). This means the object moves in a straight line. If the path were curved, the direction would change.
Q37. Acceleration in uniform circular motion is directed:
In uniform circular motion, the acceleration is called centripetal acceleration and it is always directed towards the centre of the circle. This acceleration is responsible for changing the direction of motion.
Q38. To calculate lightning distance, we need:
To calculate the distance of lightning, we use the speed of sound and the time gap between seeing the lightning and hearing the thunder. Distance = speed of sound × time.
Q39. In uniform circular motion, which remains constant?
In uniform circular motion, the speed remains constant. However, the velocity changes because the direction keeps changing. The acceleration is also not constant in direction, and displacement keeps changing.
Q40. Speed from a distance-time graph is found by:
The slope of a distance-time graph gives the speed. It is calculated as the change in distance divided by the change in time. A steeper slope means higher speed.
Q41. The SI unit of acceleration is:
The SI unit of acceleration is metres per second squared (m/s²). This comes from velocity (m/s) divided by time (s), giving m/s².
Q42. When acceleration acts in the direction of motion, speed:
When acceleration acts in the same direction as motion, it causes the speed to increase. The object moves faster and faster over time.
Q43. The motion of a pendulum is an example of:
A pendulum swings back and forth in a regular repeating pattern. This type of motion is called oscillatory or periodic motion. It repeats itself after fixed intervals of time.
Q44. If the time gap between lightning and thunder is 10 s and speed of sound is 346 m/s, the distance of lightning is:
Distance = speed × time = 346 m/s × 10 s = 3460 m. So the lightning is approximately 3.46 km away.
Q45. When direction is not specified, the quantity referred to is:
Speed is a scalar quantity that does not require direction to be specified. Velocity, acceleration, and displacement are vector quantities and require direction to be fully described.
Q46. Distance is directly proportional to time in:
In uniform motion, distance is directly proportional to time. This means distance = constant × time. The graph is a straight line passing through the origin.
Q47. For uniform speed, the distance-time graph is a:
For uniform speed, equal distances are covered in equal time intervals. So the distance-time graph is a straight line inclined to the time axis. The slope of this line gives the speed.
Q48. In a distance-time graph, the y-axis represents:
In a distance-time graph, the y-axis (vertical axis) represents distance, and the x-axis (horizontal axis) represents time. The graph shows how distance changes with time.
Q49. The SI unit of acceleration is:
The SI unit of acceleration is metres per second squared (m/s²). This is the standard unit used in physics for measuring acceleration.
Q50. Negative acceleration is also called:
Negative acceleration means the acceleration is acting in the opposite direction to the motion. This causes the object to slow down. It is also called retardation or deceleration.