Physics-DPP-4-Law of Motion

PHYSICS Topic: LAWS OF MOTION Date: 1. A car is moving along a straight horizontal road with a speed v . If the coefficient of friction between the tyres and the road is μ . The shortest distance in which the car can be stopped is : v2 æv ö2 v2 v2 (a) 0 (b) ç 0 ÷ çèμg ø÷ (c) 0 (d) 0 2μg 2. A rough vertical board has an acceleration a along the horizontal, so that a block of mass M pressing against it does not fall. The coefficient of friction between block and the board is : (a) > a g (b) < g a (c) < a (d) > g a 3. In the arragement shown in the figure, the pulley has a mass 3 m. Neglecting friction on the contact surface, the force exerted by the supporting rope AB on the ceiling is : (a) 6 mg (b) 3 mg (c) 4 mg (d) none of the above 4. A man of mass 50 kg stands on a frame of mass 30 kg. He pulls on a light rope which passes over a pulley. The other end of the rope is attached to the frame. For the system to be in equilibrium what force man must exert on the rope ? (a) 40 g (b) 80 g (c) 30 g (d) 50 g 5. A wooden box of mass 8 kg slides down an inclined plane of inclination 30o to the horizontal with a constant acceleration of 0.4 m s–2 . What is the force of friction between the box and inclined plane ? (g = 10 m/s2) (a) 36.8 N (b) 76.8 N (c) 65. 6 N (d) None of these 6. Three blocks of masses m1, m2 and m3 are connected by massless string as shown on a frictionless table. They are pulled with a force T3 = 40 N. If m1 = 10 kg, m2 = 6 kg and m3 = 4 kg, the tension T2 will be : (a) 20 N (b) 40 N (c) 10 N (d) 32 N PHYSICS Topic: LAWS OF MOTION Date: 7. A block of mass 10 kg is suspended by three strings as shown in the figure. The tension T2 is : (a) 100 N (b) 100 N (c) ´ 100 N (d) 50 N 8. A uniform rope of length l lies on a table. If the coefficient of friction is μ , then the maximum length l of the hanging part of the rope which can overhang from the edge of the table without sliding down is : 1 1 μl μl (a) μ (b) (μ + 1) (c) (μ + 1) (d) (μ – 1) 9. The upper half of an inclined plane of inclination θ is perfectly smooth while the lower half rough. A block starting from rest at the top of the plane will again come to rest at the bottom, if the coefficient of friction between the block and the lower half of the plane is given by : (a) μ = 2 tan θ (b) μ = tanθ (c) μ = 2 tan θ (d) μ = 1 tan θ 10. Consider the shown arragement. Assume all surfaces to be smooth. If N represents magnitude of normal reaction between block and wedge, then acceleration of M along horizontal is equal to : (a) N sinθ along + ve x-axis M (c) N sin θ along – ve x-axis M (b) N cosθ along – ve x-axis M N sin θ along – ve x-axis m + M PHYSICS Topic: LAWS OF MOTION Date: Answer Key 1. (d) 2. (d) 3. (d) 4. (a) 5. (a) 6. (d) 7. (d) 8. (c) 9. (a) 10. (c)