BITSAT 2014
- Exam
- BITSAT
- Year
- 2014
- Subject
- Physics
- Chapter
- Electrostatics
BITSAT 2014 · Physics · Electrostatics
A spherically symmetric gravitational system of particles has a...
A spherically symmetric gravitational system of particles has a mass density \rho=\left\{\right. where is a constant. A test mass can undergo circular motion under the influence of the gravitational field of particles. Its speed as a function of distance from the centre of the system is represented by







Options
- A

- B

- C

- D

Correct answer
C. 
Step-by-step solution
Given mass density r > R\begin{aligned}&\overrightarrow{\mathrm{F}_{\text{graw }}=\overrightarrow{\mathrm{F}_{\text{circular }}\\ &\Rightarrow \frac{\mathrm{GM}_{\text{sphere }} \times \mathrm{M}}{\mathrm{R}^{2}}=\frac{\mathrm{M}(\mathrm{e})^{2}}{\mathrm{R}}\\ &\Rightarrow \mathrm{V}^{2} \alpha \frac{\mathrm{M}_{\text{sphere }}}{\mathrm{R}} \text{ since } \mathrm{r} \leq \mathrm{R}\\ &\Rightarrow \mathrm{V}^{2} \alpha \frac{\mathrm{R}^{3}}{\mathrm{R}} \alpha \mathrm{R}^{2} \Rightarrow \mathrm{V} \alpha \mathrm{R} \quad \text{ straight line }+\mathrm{ve} \text{ slope } \end{aligned}$\mathrm{r}=\mathrm{R}$), mass density (=0 \Rightarrow) acceleration due to gravity (=0 \Rightarrow) velocity stays constant.