Verified Solution • 2025–26 Session
moderate
Q4.11: NCERT Physics - Part 1 LAWS OF MOTION 4.11 Solution: A truck starts from rest and accelerates uniformly at 2.0 m…
⚠️ Common Exam Traps & Conceptual Pitfalls
When the stone is released it keeps the truck's instantaneous horizontal speed (20 m/s) but loses the truck's horizontal acceleration; its horizontal velocity remains constant, not increasing at 2 m s⁻². Remember to treat the horizontal component as uniform motion after release.
A truck starts from rest and accelerates uniformly at 2.0 m s__. At t = 10 s, a stone is dropped by a person standing on the top of the truck (6 m high from the ground). What are the (a) velocity, and (b) acceleration of the stone at t = 11 s? (Neglect air resistance.)
Step-by-Step Verified Solution
**Answer:** (a) Horizontal velocity = 20 m/s, vertical velocity = 10 m/s downward. (b) Acceleration = 10 m/s_ downward.
**Step-by-Step Explanation:**
At t = 10 s, truck velocity = 2 _ 10 = 20 m/s. The stone retains this horizontal velocity when dropped.
(a) At t = 11 s (1 s after dropping):
- Horizontal velocity = 20 m/s (constant)
- Vertical velocity = gt = 10 _ 1 = 10 m/s downward
- Resultant velocity = �(20_ + 10_) = 22.4 m/s
(b) After dropping, only gravity acts on the stone. Acceleration = 10 m/s_ downward [citation:10].
All Questions in this Chapter
Related Learning Resources & Exam Preparation
Chapter Practice Bank
Practice all topic-wise questions from LAWS OF MOTION
Reference Textbook Solutions
Explore complete chapter exercises for NCERT Physics - Part 1
Competitive PYQ Question Bank
Browse year-wise authentic previous years' questions with solutions
Authentic CBT Mock Tests
Simulate official exam environment with live timer and percentile scoring