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Mechanics Practice Paper

2 pages, 28 questions, 26 questions with responses, 46 total responses,    0    0
Prerak Modia
S N Kansagra School (SNK), Rajkot
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SN Kansagra School MECHANICS UNIT TEST Standard: 10 Maximum Marks: 40 Date: 31st August 2016 Time: 60 minutes Question 1 a) Mention one unit of energy, apart from joule, that is used to express the following. [2] b) A ring is melted and made into a sphere. Describe what happens to its centre of gravity. [2] c) Define kgf. How is it related to the SI unit of force? [2] i. Heat energy ii. Electrical energy iii. Energy released on combustion of fat iv. Energy of an electron d) Give an example of a Class 1 lever whose mechanical advantage is lesser than 1. Describe the benefit of the machine named by you. [2] e) The number of teeth on the driver and the follower gear are 36 and 12 respectively. i. What is the use of such a gear train? [1] ii. Justify your answer to the question above. [1] a) A ball is thrown upwards. Explain why the work done by the force of gravity is negative. [2] Question 2 b) A ball is dropped from a height of 4 m. i. What is the maximum height to which the ball can bounce back after hitting the ground? [1] ii. Why is the actual height lesser than the one stated by you above? c) Why is the mechanical advantage of an inclined plane always greater than 1? [1] [2] d) A metal ball is placed upon a compressed spring. Explain why the metal ball accelerates when the spring is released. [2] e) Why is centrifugal force said to be a fictitious force? [2] Question 3 a) A machine displaces a load of 125 kgf through a distance of 0.3 m when an effort of 12.5 kgf acts through a distance of 4 m. Calculate the velocity ratio, mechanical advantage and the efficiency of the machine. [3] b) Two forces of 20 N each act at the 0 cm and 100 cm mark of a metre rule respectively as shown below. 20 N 100 cm 0 cm 20 N i. Calculate the moment produced. ii. A force at the 70 cm mark brings the rule to equilibrium. Determine the magnitude of this force. [1] [2] [2] c) A 1000 kg car races from 10 m.s- 1 to 20 m.s- 1 in 12 seconds. i. Calculate the power output of the car. ii. With the same power, how much time will the car take to go from 20 m.s- 1 to 30 m.s- 1? [2] Question 4 a) A wooden crate of mass 50 kg is to be lifted to a height of 10 m. i. ii. Which of the machines should to be used for this purpose a plank inclined at 30 with horizontal or a single movable pulley? Assume that friction in both is zero. [1] Justify your answer. [2] i. Determine the velocity of the ball at the base of the inclined plane. [2] ii. Why is the actual velocity of the ball lesser than the one calculated? [1] b) A ball is rolled on an inclined plane from a height of 3.6 m. c) A man uses a pulley system of 5 pulleys to lift a load of 3600 N. If the effort applied was 800 N, i. Determine the mechanical advantage of the pulley system. [1] ii. Determine the efficiency of the pulley system. [1] iii. Determine the resistance due to the weight of the movable block and friction. [2]

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