Tag: application of newton's law of motion

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Questions Related to application of newton's law of motion

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

Time period of simple pendulum in a satellite is

  1. Infinite

  2. Zero

  3. 2 sec

  4. Cannot be calculated
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Time period of simple pendulum is given by:
$\displaystyle T = 2\pi \sqrt{\frac{l}{g}}$
where l is the length of the pendulum.
Inside a satellite, $g = 0$
Hence, period will be infinite which means there will be no oscillation.

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

The percentage increase in earth's angular velocity so that all bodies lying on the equator feel weightlessness is nearly:

  1. 17%
  2. $\dfrac{100}{17}$%

  3. 1600%

  4. 1700%
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Weightlessness at the equator occurs when the centripetal acceleration equals gravity: omega^2 * R = g. Current omega = sqrt(g/R). To feel weightless, omega' = sqrt(g/R). Wait, the current angular velocity is such that omega^2 * R is much smaller than g. The required increase is to make omega'^2 * R = g. The ratio omega'/omega = sqrt(g/R) / (v/R) = ... The percentage increase is approximately 17%.

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

For satellite in elliptical orbit which of the following quantities does not constant 

  1. Angular momentum

  2. Momentum

  3. Areal velocity

  4. Total Energy
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In an elliptical orbit, the gravitational force is central, so angular momentum and areal velocity (Kepler's second law) are conserved. Total energy is also conserved. However, the velocity vector changes in both magnitude and direction, so linear momentum is not constant.

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

A person sitting in a chair in a satellite feels weightless because

  1. the earth does not attract the object in a satellite.

  2. the normal force by the chair on the parson balance the earht's attraction.

  3. the normal force is zero.

  4. the person is satellite is not accelerated.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As a person sits in a chair $($ on Earth's surface $)$, he will experience two forces, the force of the Earth's gravitational field pulling him downward toward the Earth and the force of the chair pushing him upward. The upward chair force is sometimes referred to as a normal force.
If there were no upward normal force acting upon body, body would not have any sensation of the weight. Without the contact force $($ the normal force $)$, there is no means of feeling the non-contact force $($ the force of gravity $)$.
Hence, A person sitting in a chair in a satellite feels weightless because normal force is zero.

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

To overcome the effect weightlessness in an artificial satellite

  1. the satellite is rotated around its axis with compartment of astronaut at the centre of the satellite.

  2. the satellite is shaped like wheel.

  3. the satellite is rotated around and around till weightlessness disappears.

  4. the compartment of astronaut is kept on the periphery of rotating wheel like satellite.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

On a rotating body, as we move away from center of rotation the centrifugal force increases. So, the centrifugal force is maximum at the periphery of a rotating wheel. Thus, having the astronaut room there would solve some of the weightlessness problem in satellite.

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

The time period of a second's pendulum inside a satellite will be

  1. zero
  2. $1$ sec
  3. $2$ sec

  4. infinite
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

time period $\propto \sqrt { \cfrac { l }{ g }  } $ , as in the satellite there will be no gravity so the time period will be infinite.(logical explanation. : without gravity there will be no force on pendulum so it will not move a bit even in infinite time.)

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

In an earth satellite moving in a circular orbit, a piece of metal weighing $16g$ (on the earth) is weighed by a spring balance while the metal is suspended in water. If the relative density of the metal is $8$, what weight will be recorded?

  1. $-2$ g

  2. zero
  3. $2$ g
  4. $14$ g
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the satellite the spring is in free fall so no weight will be recorded.

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

The radius and mean density of the earth are $R$ & $p$ respectively . the critical orbital speed of a satellite for a low altitude orbit is 

  1. $ 2 \sqrt {\dfrac { \pi G p}{3R}} $
  2. $ 2R \sqrt {\dfrac { \pi Gp}{3}} $
  3. $ 2R \sqrt {\dfrac {2 \pi G p}{3}} $
  4. $ 2R \sqrt {\dfrac { \pi Gp}{2}} $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Orbital speed v = sqrt(GM/R). Mass M = density * volume = p * (4/3) * pi * R^3. Substituting M: v = sqrt(G * p * 4/3 * pi * R^3 / R) = sqrt(4/3 * pi * G * p * R^2) = 2R * sqrt(pi * G * p / 3).

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

An astronaut, inside an earth satellite, experiences weightlessness because

  1. no external force is acting on him

  2. he is falling freely

  3. no reaction is exerted by the floor of the satellite

  4. he is far away from the earth's surface
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

For an earth satellite moving in a circular orbit, centripetal force required for its circular motion is provided by the gravitational force exerted by earth on it.
 It means resultant force on the astronaut is equal to the gravitational force exerted by earth on him. Hence, no reaction is exerted by floor of the satellite on him.
In other words, his acceleration towards earth centre (centripetal acceleration) is exactly equal to acceleration caused by the gravitational force alone.
Hence, options (b) and (c) are correct.