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NEET PHYSICSMedium

The height yy and the distance xx along the vertical plane of a projectile on a certain planet (with no surrounding atmosphere) are given by y=(8t5t2)y = (8t - 5t^2) meter and x=6tx = 6t meter, where tt is in second. The velocity with which the projectile is projected is:

A

8 m/sec

B

6 m/sec

C

10 m/sec

D

Not obtainable from the data

Step-by-Step Solution

  1. Velocity Components: The velocity of a particle is defined as the time rate of change of its position. The components of velocity are given by vx=dxdtv_x = \frac{dx}{dt} and vy=dydtv_y = \frac{dy}{dt} .
  2. Differentiate Position Equations: Given x=6tx = 6t, the horizontal velocity is vx=ddt(6t)=6 m/sv_x = \frac{d}{dt}(6t) = 6 \text{ m/s}. Given y=8t5t2y = 8t - 5t^2, the vertical velocity is vy=ddt(8t5t2)=810t m/sv_y = \frac{d}{dt}(8t - 5t^2) = 8 - 10t \text{ m/s}.
  3. Initial Velocity (at t=0): The projectile is projected at time t=0t = 0. Substituting t=0t=0 into the velocity components: vx0=6 m/sv_{x0} = 6 \text{ m/s}. vy0=810(0)=8 m/sv_{y0} = 8 - 10(0) = 8 \text{ m/s}.
  4. Calculate Resultant Velocity: The magnitude of the initial velocity (speed of projection) is: v=vx02+vy02=62+82=36+64=100=10 m/sv = \sqrt{v_{x0}^2 + v_{y0}^2} = \sqrt{6^2 + 8^2} = \sqrt{36 + 64} = \sqrt{100} = 10 \text{ m/s} .
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