A body is projected vertically upwards with initial velocity u. The time taken to reach maximum height is: MCQ with Answer and Explanation

A body is projected vertically upwards with initial velocity u. The time taken to reach maximum height is:
A. u/(2g)
B. g/u
C. 2u/g
D. u/g
Answer: Option D
Solution (By JKExamLibrary)
At maximum height, final velocity v = 0. Using v = u - gt (taking upward positive), 0 = u - gt ⇒ t = u/g. This is time of ascent. Total time of flight would be 2u/g. The equation derives from Newton's first equation of motion under constant acceleration g downward. Memory aid: Time to peak = initial velocity / gravitational acceleration. This fundamental result appears in projectile motion problems. Competitive exams often combine this with energy conservation or symmetry concepts for advanced questions.

This question belongs to: Science Physics

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Question #1 Report Error
Two bodies A and B start from the same point with velocities 10 m/s and 15 m/s respectively in the same direction. If B starts 2 seconds after A, the time after which B catches A is:
A. 10 s
B. 8 s
C. 6 s
D. 4 s

Correct Answer: Option C


Explanation:
When B starts, A has already traveled 10 m/s × 2 s = 20 m. Relative velocity of B w.r.t A = 15 - 10 = 5 m/s. Time to cover 20 m gap at 5 m/s relative speed = 20/5 = 4 s after B starts. Since B started 2 s late, total time from A's start = 2 + 4 = 6 s. Alternatively, equate distances: 10t = 15(t-2) ⇒ 10t = 15t - 30 ⇒ t = 6 s. This relative motion approach simplifies pursuit problems. Memory tip: In same-direction motion, use relative velocity = |v₁ - v₂|. Frequently tested in kinematics sections of competitive exams.

This question belongs to: Science Physics
Question #2 Report Error
Projectile horizontal range maximum at angle:
A. 30°
B. 45°
C. 90°
D. 60°

Correct Answer: Option B


Explanation:
Range R = u²sin(2θ)/g. sin(2θ) maximum (=1) when 2θ=90° ⇒ θ=45°. Standard result for level ground projection. Memory aid: 'Max range at 45°; max height at 90°'. Projectile motion fact frequently tested in competitive exams.

This question belongs to: Science Physics
Question #3 Report Error
The energy stored in an inductor of inductance L carrying current I is
A. L²I
B. ½LI
C. ½LI²
D. LI²

Correct Answer: Option C


Explanation:
Magnetic energy stored = ½ L I², analogous to capacitor energy ½ C V². L is inductance in henry (H). Energy stored in magnetic field.

This question belongs to: Science Physics