 ## Why does a block of plastic released under water come up to the surface of water ?

[question] Question. Why does a block of plastic released under water come up to the surface of water ? [/question] [solution] Solution: Density of plastic block is less than the density of water. Thus, when it floats, it is partially immersed in water such that its weight gets balanced with the buoyant force acting on it. When it is put completely in water, buoyant force on it becomes more than its weight. Thus, when it is released, it comes up to the surface of the water due to a net upward fo...

## In what direction does the buoyant force on an object immersed in a liquid act ?

[question] Question. In what direction does the buoyant force on an object immersed in a liquid act ? [/question] [solution] Solution: An object immersed in a liquid experiences a buoyant force in upward direction. [/solution]...

## A ball thrown up vertically returns to the thrower after 6 s. Find.

[question] Question. A ball thrown up vertically returns to the thrower after 6 s. Find. (a) the velocity with which it was thrown up (b) the maximum height it reaches, and (c) its position after 4 s (take g = 10 m/s2) [/question] [solution] Solution: (a) The ball returns to the thrower in 6 s, thus, the time for its upward journey = 6 ÷ 2 = 3 s For the upward motion of ball, initial velocity u = ? ; final velocity v = 0 ( $\because$ Ball comes to rest) Time, t = 3 s Acceleration due to gravity,...

## Gravitational force acts on all objects in proportion to their masses.

[question] Question. Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object ? [/question] [solution] Solution: A freely falling object of any mass falls under the action of gravity given by $g=\frac{G M}{r^{2}}$, where $^{\prime} G^{\prime}$ is constant of gravitation, M is mass of earth, r is the distance between the object and the centre of earth. Thus, the acceleration due to gravity is independent of the mass o...

## How does the force of gravitation between two objects

[question] Question. How does the force of gravitation between two objects change when the distance between them is reduced to half ? [/question] [solution] Solution: When all other variables remain constant, the force of gravitation is inversely proportional to the square of distance between the two objects. $F \propto \frac{1}{r^{2}} \Rightarrow \frac{F^{\prime}}{F}=\frac{r^{2}}{\left(\frac{r}{2}\right)^{2}}=\frac{4 r^{2}}{r^{2}}=4$ $\therefore$ The force of gravitation increases 4 times. [sol...

## What are the differences between the mass of an object and its weight ?

[question] Question. What are the differences between the mass of an object and its weight ? [/question] [solution] Solution: [/solution]...

## What do you mean by acceleration due to gravity?

[question] Question. What do you mean by acceleration due to gravity? [/question] [solution] Solution: The acceleration produced in a body due to force of gravity is called acceleration due to gravity. It is denoted by g. The value of acceleration due to gravity is taken as 9.8 ms–2 at the sea level. [/solution]...

## What do you mean by free fall ?

[question] Question. What do you mean by free fall ? [/question] [solution] Solution: When an object moves with a constant acceleration, under the influence of force of gravitation of the earth only, the object is said to have free fall. [/solution]...

## Write the formula to find the magnitude of the gravitational force between t.

[question] Question. Write the formula to find the magnitude of the gravitational force between the earth and an object on the surface of the earth. [question] [solution] Solution: $\mathrm{F}_{\mathrm{g}}=\frac{\mathrm{GMm}}{\mathrm{R}^{2}}$ Where G is gravitational constant, M is the mass of the earth, m is the mass of the object, R is the distance between the centre of the object and the centre of the earth radius of earth. [solution]...

## State the universal law of gravitation.

[question] Question. State the universal law of gravitation. [/question] [solution] Solution: Every body in this universe attracts every other body with a force, which is directly proportional to the product of their masses and inversely proportional to the square of distance between their centres [/solution]...