Question

A projectile is projected with initial velocity
(61 +8j m/s, from the ground. The velocity when
it is about to hit the ground is (assuming y-axis is
along vertical direction)
[NCERT Pg. 78]
(1) 6i +8j m/s
(2) 61-8j m/s
(3) -61 - 8j m/s
(4) -6i +8j m/s​

Answer 1

Answer:

bcoz when it hit the ground

its +y axis change to - y acix but x do not change

so ans. is 2

Answer 2

Given:

Initial velocity of projectile is $6\hat{i}+8\hat{j}$.

To find:

Velocity vector when the projectile hits ground?

Calculation:

• First of all, projectile motion is an oblique, parabolic 2D motion.

• Here, Gravitational Acceleration (i.e. g = 9.8 m/s²) acts only in the -Y axis direction. So, X axis doesn't experience any acceleration.

• So, velocity of projectile changes only in the Y axis , but remains constant in the X axis.

• Hence, when the projectile hits the ground, the Y component of velocity will be reversed in direction (but same magnitude) and X component will remain same as initial velocity.

• Final answer : $6\hat{i}-8\hat{j}$ will be ground hitting velocity.

Option 2) is correct ✔️