© 2026 LearnInShort
Two Motions, One Idea: Direction Changes Matter
A cricket ball hit into the air and a stone whirled on a string look unrelated, yet both are Newton's laws at work. In circular motion the speed can stay fixed while the direction keeps changing, so the body is still accelerating. In projectile motion a horizontal velocity that never changes is combined with a vertical motion under gravity.
Exams love these topics because a few formulas decide everything, and a few classic misconceptions decide the wrong answers: 'centrifugal force pulls outward' and 'a heavier ball falls faster'.
Master three habits: always ask which direction the acceleration points, split projectile motion into horizontal and vertical parts, and never mix degrees with radians. The next cards give the formulas, worked numbers and the exact traps.
1. In uniform circular motion, the acceleration of the body is directed:
2. A 2 kg mass moves at 3 m/s on a circle of radius 1.5 m. The centripetal force on it is:
3. For the same speed of projection, which angle gives the same range as 30°?
4. A ball is thrown at 20 m/s at 60° above the horizontal. Its speed at the highest point is:
5. A projectile is launched at 20 m/s at 30° to the horizontal (g = 10 m/s²). Its maximum height is:
6. A stone whirled in a horizontal circle on a string is released when the string breaks. The stone then moves:
7. One ball is dropped and another is thrown horizontally from the same height at the same instant. Which reaches the ground first?
8. A wheel rotates at 120 revolutions per minute. Its angular speed is: