i. The work done will be zero when the angle between the force and the distance is




... Answer is (c)  90°
Work is done when a force acting on a body displaces it in the direction of the force. Hence W = Fx S = FS cosθ, at θ = 90⁰ then W = FS cos90⁰ = FS x 0 = 0 J (cos90⁰ =0)


ii. If the direction of motion of the force is perpendicular to the direction of motion of the body, then the work done will be




... Answer is (c)  zero
Work is done when a force acting on a body displaces it in the direction of the force. Hence W = Fx S = FS cosθ When force is perpendicular to the direction of motion of the body i.e. θ = 90⁰ the Work W = FS cos90⁰ = 0 J


iii. If the velocity of the body becomes double, then its kinetic energy will




... Answer is (c) become four times
K.E. = (1/2)mv² When velocity of the body becomes double K.E. = (1/2)m(2v)² = 4 K.E


iv. The work done in lifting a brick of mass 2 kg through a height of 5 m above ground will be




... Answer is (d) 100 J
Work Done W = F S = mgh = 2x10x5 = 100 J (Taking g=10m/s²)


v. The kinetic energy of a body of mass 2 kg is 25 J. Its speed is




... Answer is (a) 5 ms^-1
K.E. = (1/2) mv² v = √ 2K.E/m v = √2x25/2 =√25=5m/s


vi. Which one of the following converts light energy into electrical energy?




... Answer is (c) Photocell
The light incident on the photocell gives out an electric current. So, a photocell converts light energy into electrical energy.


vii. When a body is lifted through a height h, the work done on it appears in the form of its: :




... Answer is (b) potential energy
When a body of mass m is lifted through a height h, the work done on it appears in the form of its Potential Energy P.E. = mgh


viii. The energy stored in coal is




... Answer is (c)  chemical energy
Chemical energy is the energy that is stored in the bonding of atoms and molecules. Batteries, biomass, petroleum, natural gas, and coal are examples of chemical energy. Chemical energy is converted to thermal energy (on breaking of bonding between the atoms or Molecules), when people burn coal/wood in a fireplace or burn gasoline in a car's engine.


ix. The energy stored in a dam is




... Answer is (b)  potential energy
The water is stored in dams at a certain height so it has Potential Energy and then the down flow is made to run a turbine i.e. partly changes into electrical energy


x. In Einstein's mass-energy equation, c is the




... Answer is (b)  speed of light
The equation E = mc^2 is Einstein's mass-energy equation. It means "energy is equal to the product of mass and squared off the speed of light ." It shows that energy (E) and mass (m) are interchangeable; they are different forms of the same thing and (c) represents the speed of light.


xi. The Rate of doing work is called




... Answer is (c)  power
The rate of doing work is called Power P = W/t. Its unit is a watt.



VIP Note: If you have Learned the above MCQs, then examine yourself by taking this Simple MCQS Quiz (Click here to play the Quiz)


 
Unit-6 Work and Energy
⇑
9th Class MCQs Quizzes LIST

⇑
Unit-5 ⇚   9th Physics Content List   ⇛   Unit-7


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