All 8 short questions of 9th Class Physics Chapter 2, Kinematics, with exam-ready answers in the book's words. Punjab Board new syllabus.
Exam-ready answers. Learn the meaning, then write them in your own words.
A scalar quantity is fully described by its magnitude alone, for example mass, time and speed.
A vector quantity needs both magnitude and direction to be fully described, for example displacement, velocity and force.
| Scalars | Vectors |
|---|---|
| Distance | Displacement |
| Speed | Velocity |
| Mass | Weight |
| Time | Acceleration |
| Energy | Force |
Draw the vectors to scale, joining the tail of each vector to the head of the one before it. The resultant is the vector drawn from the tail of the first vector to the head of the last vector.
A distance-time graph shows how the distance covered by a body changes with time (time on the x-axis, distance on the y-axis). Its gradient gives the speed.
A speed-time graph shows how the speed of a body changes with time (time on the x-axis, speed on the y-axis). Its gradient gives the acceleration and the area under it gives the distance.
No. Since every object falls with the same acceleration g (about 10 m s⁻²), whatever its mass, a heavy and a light object dropped together from the same height reach the ground together.
In everyday life a feather or a sheet of paper falls more slowly only because air resistance affects it much more; in a vacuum it would fall as fast as a stone.
The direction is stated separately: in words (for example "20 m s⁻¹ towards the north"), as an angle (for example "at 30° to the x-axis"), or with a + or − sign for the two directions along a straight line.
Not necessarily. Velocity has both magnitude and direction. If the body moves in a straight line, its velocity is uniform too.
But if its direction changes, for example a car going round a circular track at a steady 40 km h⁻¹, its velocity changes all the time even though its speed is uniform.
(i) No. Acceleration is the rate of change of velocity. If the velocity is constant, it does not change, so the acceleration is zero.
(ii) Yes. If the speed is constant but the direction keeps changing, as in circular motion, the velocity changes, so the body is accelerating.
