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# NEET Physics  Laws of Motion  Practice Q & A

1. Three blocks A, B and C of masses 4 kg, 2 kg and 1 kg respectively, are in contact on a frictionless surface, as shown. If a force of 14 N is applied on the 4 kg block, then the contact force between A and B is

 2 N 6 N 8 N 18 N

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2. A plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches 30º, the box starts to slip and slides 4.0 m down the plank in 4.0 s. The coefficients of static and kinetic friction between the box and the plank will be, respectively
kinetic friction between box and plank.jpg" alt="static and kinetic friction between box and plank" style="margin:0 auto;" />

 0.4 and 0.3 0.6 and 0.6 0.6 and 0.5 0.5 and 0.6

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3. Maximum acceleration of the train in which a 50 kg box lying on its floor will remain Stationery
(Given : Co–efficient of static friction between the box and the train’s floor is 0.3 and g = 10 ms–2)

 5.0 ms–2 3.0 ms–2 1.5 ms–2 15 ms–2

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4. Given in the figure are two blocks A and B of weight 20 N and 100 N, respectively. These are being pressed against a wall by a force F as shown. If the coefficient of friction between the blocks is 0.1 and between block B and the wall is 0.15, the frictional force applied by the wall on block B is

 100 N 80 N 120 N 150 N

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5. A block of mass m is placed on a surface with a vertical cross section given by $y = \dfrac{x_3}{6}$. If the coefficient of friction is 0.5, the maximum height above the ground at which the block can be placed without slipping is

 $\dfrac{2}{3}$m $\dfrac{1}{3}$m $\dfrac{1}{2}$m $\dfrac{1}{6}$m

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6. A machine gun fires a bullet of mass 40 g with a velocity 1200 ms–1. The man holding it can exert a maximum force of 144 N on the gun. How many bullets can he fire per second at the most?

 One Two Three Four

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7. A stone of mass 0.05 kg is thrown vertically upwards. What is the direction and magnitude of net force on the stone during its upward motion?

 0.98 N vertically downwards 0.49 N vertically downwards 9.8 N vertically downwards 0.49 N vertically upwards

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8. The force F acting on a particle of mass m is indicated by the force–time graph shown below. The change in momentum of the particle over the time interval from zero to 8 s is

 24 Ns 20 Ns 12 Ns 6 Ns

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9. The minimum force required to start pushing a body up a rough (frictional coefficient μ) inclined plane is F1 while the minimum force needed to prevent it from sliding down is F2. If the inclined plane makes an angle θ from the horizontal such that tan θ = 2μ, then the ratio F1/F2 is

 1 2 3 4

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10. A rocket with a lift–off mass 3.5 × 104 kg is blasted upwards with an initial acceleration of 10 m/s2. Then the initial thrust of the blast is

 1.75 × 105 N 3.5 × 105 N 7.0 × 105 N 14.0 × 105 N

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