When a particle is undergoing motion, the diplacement of the particle has a magnitude that is equal to or smaller than the total distance travelled by the particle. In many cases the displacement of the particle may actually be zero, while the distance travelled by it is non-zero. Both these quantities, however depend on the frame of reference in which motion of the particle is being observed. Consider a particle which is projected in the earth's gravitational field, close to its surface, with a speed of `100sqrt(2) m//s`, at an angle of `45^(@)` with the horizontal in the eastward direction. Ignore air resistance and assume that the acceleration due to gravity is `10 m//s^(2)`.
Consider an observer in frame D (of the previous question), who observes a body of mass 10 kg acelerating in the upward direction at `30 m//s^(2)` (w.r.t. himself). The net force acting on this body, as observed from the ground is :-

Options

A. `400 N` in the upward direction
B. `300 N` in the upward direction
C. `200 N` in the upward direction
D. `500 N` in the upward direction

Answer

C

Explanation

`underset(*)(uarr)a_(b)=20 m//s^(2), overset(*)(darr)a_(D)=10 m//s^(2)`
`a_(bD)=30 m//s^(2) uarr`
`:.` Force acting on a body `=10xx20=200N`