Free Study Material

NCERT Solutions

NCERT Books

Revision Notes

Practice Problems

This is one of our many quizzes on potential energy. Click on this to access more such competitive quizzes on potential energy.

Potential energy Quiz 2

physics

Select true or false from the following. $ \\ $ 1. The potential energy will always be negative, zero or positive. $ \\ $ 2. The kinetic energy will always be negative, zero or positive. $ \\ $ 3. The kinetic energy and potential energies are vector quantities. 

The mass and the square of velocity cannot be negative in the equation of kinetic energy. 

  The potential energy will be having values as negative, zero or positive. $ \\  E=\dfrac{1}{2}m{{v}^{2}}$ The mass and the square of velocity cannot be negative. Therefore the kinetic energy can’t have a negative value. All kinds of energies are scalar quantities only.

 Fill in the blanks for the following. $ \\ $ When a weight lifter is taking up weight and walking through the stage. He is holding the weight of mass $100\,kg$ normal to the direction in which he walks. In this situation…….. the amount of energy has been lost by the man. 

Energy is the dot product of force and the displacement. 

 As the weight he is carrying is normal to the direction of his motion, $  \\  \theta =90^{\circ}  \\  \Rightarrow F\cdot S=FS\cos \theta   \\  \Rightarrow FS\cos 90^{\circ} =0$

The clocks sweep out an area $6\,{{m}^{2}}$ with a velocity of $3\text{ m}m{{s}^{-1}}$. This velocity is perpendicular to the circular shaped clock. Assume that the clock has been placed inside water with density $1.33\text{ kg}{{m}^{-3}}$ at a height $4\,m$ for a time $15\,s$. What will be the potential energy of the clock? 

The mass can be substituted as the product of area, velocity, density and time taken. 

 $\text{Potential energy, } U=mgh  \\  \Rightarrow U=\left( Av\rho t \right)gh  \\  \Rightarrow U=\left( 6\times 3\times {{10}^{-3}}\times 1.33\times 15 \right)\times g\times 4  \\  \Rightarrow U=1.44g$

 The force at which a cricketer hits the bat has been given as, $F=\left( 3\hat{i}+\hat{j}-2\hat{k} \right)$. The velocity has been mentioned as $V=\left( 4\hat{i}+2\hat{j}+4\hat{k} \right)$. If the cricketer took $5\,s$ to complete this action, calculate the energy he used up here? 

The energy can be found by taking the product of power and time taken. 

 $\text{Power, } P=F\cdot V  \\  \Rightarrow P=\left( 3\hat{i}+\hat{j}-2\hat{k} \right)\cdot \left( 4\hat{i}+2\hat{j}+4\hat{k} \right)  \\  \Rightarrow P=12+2-8=6W  \\  \text{The energy used up will be, } \\  U=Pt  \\  \Rightarrow U=6\times 5  \\  \therefore U=30\,J$

 A boy who is curious about physics saw a coincidence that the potential energy of a mango of mass $200\,g$ on a tree at a height of $5\,m$ is having same potential energy as that of the spring in his hand which he displaced it for a distance of $2\,mm$. What would be the spring constant of the spring? 

The energy of a mango on a tree will be the potential energy.

 $\dfrac{1}{2}K{{X}^{2}}=mgh  \\  \Rightarrow \dfrac{1}{2}\times K\times {{\left( 2\times {{10}^{-3}} \right)}^{2}}=200\times {{10}^{-3}}\times 9.8\times 5  \\  \Rightarrow K=4.9\times {{10}^{6}}\,N{{m}^{-1}}\approx 5\times {{10}^{6}}\,N{{m}^{-1}} $