JEE Main20208 Jan 2020Evening ShiftPhysicsMotion in Two DimensionsActual
A particle moves such that its position vector r → t = cos ⁡ ω t i ^ + sin ⁡ ω t j ^ where ω is a constant and t is time. Then which of the following statements is true for the velocity v → t and acceleration a → t of the particle:
Options
- Av → is perpendicular to r → and a → is directed away from the origin
- Bv → and a → both are perpendicular to r →
- Cv → and a → both are parallel to r →
- Dv → is perpendicular to r → and a → is directed towards the origin
Correct answer
D. v → is perpendicular to r → and a → is directed towards the origin
Step-by-step solution
r → = cos ω t i ^ + sin ω t j ^ v → = d r → d t = ω - sin ω t i ^ + cos ω t j ^ a → = d v → d t = - ω 2 cos ω t i ^ + sin ω t j ^ a → = - ω 2 r → ∴ a → is antiparallel to r → v → . r → = ω - sin ω t cos ω t + cos ω t sin ω t = 0 So v → ⊥ r →