Question

Assertion :If a body is projected obliquely at angle $\theta$ above horizontal with initial speed $v$ then its speed at the instant when its velocity makes an angle $\alpha$ above the horizontal is $\frac{vcos\theta }{cos\alpha }$ Reason: Horizontal component of velocity of projectile remains constant.

• A. Both Assertion and Reason are true and the Reason is correct explanation of the Assertion.
• B. Both Assertion and Reason are true, but Reason is not correct explanation of the Assertion.
• C. Assertion is true, but the Reason is false.
• D. Assertion is false, but the Reason is true.

Answer 1

The correct option is A Both Assertion and Reason are true and the Reason is correct explanation of the Assertion.

At any time $v_x=v\cos \theta \Rightarrow$constant.

Assume velocity is $v^{\prime }$ at any moment making an angle $\alpha$ with horizontal.

Hence, $v_x=v\cos \theta =v^{\prime }\cos \alpha$
$\Rightarrow v^{\prime }=\frac{v\cos \theta }{\cos \alpha }$