Question

The driver of a car moving towards a rocket
launching with a speed of 6 m/s observed that
the rocket is moving with speed of 10 m/s.
The upward speed of the rocket as seen by
the stationary observer is nearly
1) 4 ms-1
2) 6 ms-1
3) 8 ms -1
4) 11 ms1​

Answer 1

Given that,

Speed of car $v_{C}=6\ m/s$

Speed of rocket $v_{RC} = 10\ m/s$

We need to calculate the speed of the rocket as seen by  the stationary observer

Using formula of velocity

$v_{R}=\sqrt{v_{C}^2+v_{RC}^2-2v_{C}v_{RC}\cos90}$

Put the value into the formula

$v_{R}=\sqrt{6^2+10^2-2\times6\times10\cos90}$

$v_{R}=\sqrt{36+100}$

$v_{R}=\sqrt{136}$

$v_{R}=11\ m/s$

Hence, The speed of the rocket as seen by  the stationary observer is 11 m/s.

(4) is correct option.