NEET Free Online Mock Test - 2019

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# NEET Physics  Work, Energy & Power  Practice Q & A

1. A ball is thrown vertically downwards from a height of 20 m with an initial velocity v02. It collides with the ground, loses 50 percent of its energy in collision and rebounds to the same height. The initial velocity v0 is (Take g = 10 ms–2)

 10 ms–1 14 ms–1 20 ms–1 28 ms–1

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2. A bullet of mass 10 g moving horizontally with a velocity of 400 ms–1 strikes a wood block of mass 2 kg which is suspended by light inextensible string of length 5 m. As a result, the centre of gravity of the block found to rise a vertical distance of 10 cm. The speed of the bullet after it emerges out horizontally from the block will be

 100 ms–1 80 ms–1 120 ms–1 160 ms–1

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3. A block of mass 10 kg moving in $x$ direction with a constant speed of 10 ms–1, is subjected to a retarding force F = 0.1$x$ J/m during its travel from $x$ = 20 m to 30 m. Its final KE will be

 475 J 450 J 275 J 250 J

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4. A body of mass 1 kg begins to move under the action of a time dependent force F = 2tî + 3t2ĵ)N, where î and ĵ are unit vectors along $x$ and y axis. What power will be developed by the force at the time t?

 (2t3 + 3t4) W (2t3 + 3t5) W (2t2 + 3t2) W (2t2 + 4t4) W

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5. An athlete in the Olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

 2 × 105 J – 3 × 105 J 20,000 J – 50,000 J 2,000 J – 5,000 J 200 J – 500 J

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6. Statement–1 : Two particles moving in the same direction do not lose all their energy in a completely inelastic collision.
Statement–2 : Principle of conservation of momentum holds true for all kinds of collisions.

 Statement–1 is true, Statement–2 is false Statement–1 is true, Statement–2 is true; Statement–2 is the correct explanation of Statement–1 Statement–1 is true, Statement–2 is true; Statement–2 is the not the correct explanation of Statement–1 Statement–1 is false, Statement–2 is true

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7. A nucleus at rest splits into two nuclear parts having radii in the ratio 1 : 2. Their velocities are in the ratio

 4 : 1 8 : 1 2 : 1 6 : 1

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8. A force F acting on an object varies with distance $x$ as shown here. The force is in N and $x$ in m. The work done by the force in moving the object from $x$ = 0 to $x$ = 6 m is

 18.0 J 13.5 J 4.5 J 9.0 J

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9. A bob of mass M is suspended by a massless string of length L. The horizontal velocity V at position A is just sufficient to make it reach the point B. The angle θ at which the speed of the bob is half of that at A, satisfies

 $\theta = \dfrac{\pi}{4}$ $\dfrac{\pi}{4}< \theta < \dfrac{\pi}{2}$ $\dfrac{\pi}{2}< \theta < \dfrac{3\pi}{4}$ $\dfrac{3\pi}{4} < \theta < \pi$

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10. A block (B) is attached to two unstretched springs S1 and S2 with spring constants k and 4k, respectively (see figure I). The other ends are attached to identical supports M1 and M2 not attached to the walls. The springs and supports have negligible mass. There is no friction anywhere. The block B is displaced towards wall 1 by a small distance $x$ (figure II) and released. The block returns and moves a maximum distance y towards wall 2. Displacements $x$ and y are measured with respect to the equilibrium position of the block B. The ratio y/x is

 4 2 1/2 1/4

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