Tag: concept of force and its unit

Questions Related to concept of force and its unit

1 dyne is equal to

physics force concept of force and its unit force - push or pull forces

  1. 980 g wt

  2. $\displaystyle \frac{1}{980}$ g wt

  3. 980 kg wt

  4. none of these

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Correct Option: B
Explanation:

Dyne is unit of force specified in CGS system. 

So $ 1 dyne= 10^{-5} N $
And $ 1 N = \dfrac{1}{9.80} kg $
Now,
$ 1 dyne= \dfrac{1}{9.80} \times 10^{-5}  kg$


Changing kg into grams,
 $ 1 dyne = \dfrac{1}{9.80} \times 10^{-5}  \times 10^3 g $
So,
 $ 1 dyne= \dfrac{1}{980}g  \ wt $.

Which of the following sets of concurrent forces may be in equilibrium?

physics force concept of force and its unit force - push or pull forces

  1. $\displaystyle { F } _{ 1 }=3N,{ F } _{ 2 }=5N,{ F } _{ 3 }=1N$

  2. $\displaystyle { F } _{ 1 }=3N,{ F } _{ 2 }=5N,{ F } _{ 3 }=9N$

  3. $\displaystyle { F } _{ 1 }=3N,{ F } _{ 2 }=5N,{ F } _{ 3 }=6N$

  4. $\displaystyle { F } _{ 1 }=3N,{ F } _{ 2 }=5N,{ F } _{ 3 }=15N$

Show answer
Correct Option: C
Explanation:
"Forces are in equilibrium when vector sum of these three forces is zero and they form a triangle.
For a triangle, the sum of the two sides is always greater than the third side
Therefore, $F _1 = 3N; F _2 = 5N; F _3 = 6N$

$F _1 + F _2 > F _3$

$F _2 + F _3 > F _1$

$F _3 + F _1  > F _2$


In a game of tug of war, three girls of team $A$ pull the rope with forces of $100 N$, $120 N$ and $170 N$. In team $B$, the three members pull the rope with forces of $130 N$, $150 N$ and $155 N$. Who will win the tug of war? What is the resultant force?

physics force concept of force and its unit force - push or pull forces

  1. Team $A$, $55 N$

  2. Team $B$, $55 N$

  3. Team $A$, $45 N$

  4. Team $B$, $45 N$

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Correct Option: D
Explanation:

Resultant force is nothing but the total force acting on a body including their directions. If the object is at rest or it moves with a same velocity, the resultant force should be zero. All forces are acting on same direction, resultant force should be the sum of all the forces.

In this case, the forces applied by team A are 100 N, 120 N and 170 N. The total force is 100 N+120 N+170 N = 390 N. The forces applied by tema B are 130 N, 150 N and 155 N. The total force is 130 N+150 N+155 N=435 N.
Now, both the total forces are in the opposite direction as the team are in the opposite direction. So, the resultant force is 435 - 390 = 45 N. 
Therefore, Team B will win in the game as they apply more force of 45 N.

Suppose a body that is acted on by only two forces, is accelerated. For this situation, mark the correct statement :
( Initial Velocity is non zero and in same direction as acceleration  ) 

physics force concept of force and its unit force - push or pull forces

  1. The body cannot move with constant speed

  2. The velocity can never be zero

  3. The sum of two forces cannot be zero

  4. The two forces must act in the same line

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Correct Option: A,B,C
Explanation:

If the body is accelerating, then there is a net force which drives the body. Since the body is accelerating, velocity can not be zero or moving with a constant speed. 
It is not necessary that the two forces must act in the same line however they may act in the same line.

A force F is given by $F=at+bt^2$, where t is time. The dimensions of a and b are:

physics force concept of force and its unit force - push or pull forces

  1. $[MLT^{-3}]$and$ [MLT^{-4}]$

  2. $[MLT^{-4}]$and$ [MLT^{-3}]$

  3. $[MLT^{-1}]$and$ [MLT^{-2}]$

  4. $[MLT^{-2}]$and$ [MLT^{0}]$

Show answer
Correct Option: A
Explanation:

Given that $F=at+bt^2$ where $t$ is time.


For this equation to be dimensionally correct, the each term in the right hand side should have the dimensions of $F$

Dimensional formula of $F=[ MLT^{-2}]$

$\implies aT=[ MLT^{-2}]$
$\implies$ Dimension of $a$ is $[ MLT^{-3}]$

and
$\implies bT^2=[ MLT^{-2}]$
$\implies$ Dimension of $b$ is $[ MLT^{-4}]$

Hence, option $(A)$ is correct.

What happens when two forces in the same direction, are applied on an object?

physics mechanics concept of force and its unit force - push or pull forces

  1. Forces add up.

  2. Forces subtract.

  3. Resultant force is the division of forces.

  4. None of the above.

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Correct Option: A
Explanation:

When two forces are applied on a object in the same direction, forces added up and net force increases.

When you and your friend push a table in opposite directions, it becomes difficult to move. This is because:

physics mechanics concept of force and its unit force - push or pull forces

  1. the net force becomes the sum of  the two forces.

  2. the net force becomes the difference of the two forces.

  3. the table becomes heavier.

  4. the table becomes lighter.

Show answer
Correct Option: B
Explanation:

When two forces are applied in opposite directions, the net force becomes the difference of the two. So, the net force becomes small and the table becomes difficult to move.

Fill in the blanks:

The SI unit of force is _______.

physics mechanics concept of force and its unit force - push or pull forces

  1. Pascal

  2. Kelvin

  3. Newton

  4. Celcius

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Correct Option: C
Explanation:

In SI system of units, force is expressed in Newtons ($N$).

In the game of tug-of-war, the team that pulls the rope harder wins the game. This is because:

physics mechanics concept of force and its unit force - push or pull forces

  1. the rope moves in the direction of larger force.

  2. the rope moves in the direction of the smaller force.

  3. the rope does not move at all.

  4. the rope moves in the direction of product of the forces.

Show answer
Correct Option: A
Explanation:

In a game of tug-of-war, teams apply forces in terms of pulls on the rope. On the rope, two pulls act in opposite directions. The net force becomes the difference of the two forces (pulls) and the rope moves in the direction of the larger force (pull).

When you and your friend pushes heavy table in the same direction, it becomes easier to move. This is because:

physics mechanics concept of force and its unit force - push or pull forces

  1. the net force is the sum of forces.

  2. the net force is the difference of forces.

  3. the table becomes lighter.

  4. friction reduces.

Show answer
Correct Option: A
Explanation:

When you and your friend pushes heavy table in the same direction, the force applied by you and your friend get added. So, applied forces sum up to get a larger force. Hence the table moves easily.