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This is one of our many quizzes on Force essentials. Click on this to access more such competitive quizzes on Mechanics.

Force essentials Quiz 2

physics

 What is the most essential quantity for an electrostatic force? 

  The word electrostatic means that charge at rest or charge which is not moving. Electrostatic force develops between two charges placed at a certain distance. So, charge is fundamental. 

 The force that attracts or repels. Electrostatic force is the force between two charged particles. It has a greater strength than gravity. Electrostatic forces are both attractive and repellent. If the charges are the same, that is ‘like charges’, the force will be repulsive and if they are of opposite nature, that is ‘unlike’ charges, they attract. From this, it can be easily understood that charge is the fundamental thing for an electrostatic force to happen. 

 Out of the following, Select the approximate range for short range forces.

 Forces can be classified into two categories on the basis of their range. Short range and long range forces. They are classified on the basis of distance between the centers of interacting molecules. 

  A force is placed in the category of short range forces when the particles interacting during the force are separated by a distance of ${{10}^{-15}}\,m$ or less. These types of forces normally seem to be repulsive in nature. Whereas, in long range forces, particles interacting during the force are separated by a distance of $3\times {{10}^{-10}}\,cm$ or greater.

  If 30 blocks of mass $M$ are placed on a floor to be lifted to top of a building of $2\,m$ high using a pulley mechanism. Suddenly, at $10\,m$ of height the suspension rope of pulley is broken. Then, what will be the normal force exerted on the mass by the floor ? 

  Normal force exerted on the mass by the floor will be equal to Weight of the body and weight of a body during freefall will be zero. 

Here, $M=30\times m$. Now, if the rope is broken, the elevator falls freely. So, the downward acceleration of the man in the elevator is $a=g$. Now, the force exerted by the floor on a mass = actual weight of mass − net upward force on a mass $F=Ma-Mg \\ \Rightarrow F=Mg-Mg \\ \therefore F=0\,N $ Hence, the force exerted by the floor on a man is zero.

If a man wants to move the block given in the diagram, what should be the minimum force that he should apply? <img src="https://cmds-vedantu.s3.ap-southeast-1.amazonaws.com/prod/question-sets/294024bd-9466-4bf9-aaea-380db7fcdcf01274954211743327097.png"/>

 For moving the block, the man will have to overcome static friction. So, the minimum force needed to be applied will be equal to static friction offered by the floor.

To move the block, the man will have to overcome the static friction applied by the floor on the block.Static friction is given by the formula, ${{F}_{s}}=\mu N$ Here, $N$ is the normal force and it is equal to the weight of the body. ${{F}_{s}}=\mu mg \\ \Rightarrow {{F}_{s}}=0.4\times 5\times 9.8 \\ \therefore {{F}_{s}}=19.6\,N$

 Venu was travelling through a straight road where his gravitational force was mentioned as  $64\text{ }J$.  He was moving forward with an acceleration $4\text{ }m{{s}^{-2}}$. What will be his net force ?

 The gravitational force will be the product of the mass of the person and the acceleration due to gravity. 

 $\text{The gravitational force,} \\ {{F}_{1}}=mg \\ \text{Substituting the values,} \\ \text{64=m}\times 10 \\ \Rightarrow m=6.4\text{ }kg \\ \text{The force because of the acceleration,} \\ {{\text{F}}_{2}}\text{=ma} \\ \text{Substituting the values,} \\ {{\text{F}}_{2}}\text{=6}\text{.4}\times 4 \\ \Rightarrow {{\text{F}}_{2}}\text{=}25.6\text{ }N \\ \text{The angle between the forces will be,} \\ \theta =90{}^\circ  \\ \text{Hence the net force will be,} \\ F=\sqrt{{{F}_{1}}^{2}+{{F}_{2}}^{2}+2{{F}_{1}}{{F}_{2}}\cos \theta } \\ \text{Substituting the values,} \\ \text{F=}\sqrt{{{64}^{2}}+{{25.6}^{2}}+2\times 64\times 25.6\cos 90{}^\circ } \\  \Rightarrow F=\sqrt{{{64}^{2}}+{{25.6}^{2}}} \\ \Rightarrow F=\sqrt{655.36+4096} \\ \Rightarrow F=\sqrt{4751.36} \\ \therefore F=68.93\text{ }N$