Question

A ball is thrown upwards and it returns to ground describing a parabolic path. Which of the following has the same value at the time of throw and the time of return?
I. Kinetic energy of the ball
II. Speed of the ball
III. Vertical component of velocity
IV. Horizontal component of velocity

• A. I, II and IV
• B. II and III
• C. III and IV only
• D. I, II and III

Answer 1

Answer: (A)

If we neglect air resistance, horizontal component of velocity is always same.

To find vertical component use equation,
$v_f^2=v_i^2-2g\times h,$
$v_i=u\sin \theta ,h=0$,
$v_f^2=u^2{\sin }^2\theta -0,v_f=u\sin \theta$
hence $\vec{v}=u\cos \theta \hat{i}-u\sin \theta \hat{j}$
$\therefore$ Speed is same, so K.E. is same.