Khud Ko Badlo Tumhare Liye Swath Badal Jayagi

Assignment III, 2011 Subject : Physics Date of Submission : 02.09.2011 1.

MPS : XI MM : 25

State whether the given statement is true or false and give reason. Work done in the motion of a body over a closed loop is zero for every force in nature . 1 A helicopter lifts a 72 kg astronaut 15 m vertically from the ocean by means of a cable. The acceleration of the astronaut is g/10. How much work is done by the following on the astronaut? a) The force from the helicopter. b) The gravitational force on him. Also calculate the Kinetic energy of astronaut. 3 a) A body is moving unidirectionally under the influence of a source of constant power. Show that its displacement in time ‘t’ is directly proportional to t3/2. Define coefficient of restitution.

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3.

b) 4.

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Give reason. a) Sand is thrown on tracks covered with snow in hilly areas. b) It is difficult to start motion than to maintain it. c) A locomotive does no work against granty when it is running on a level plane with a speed of 60 km/h. 3 a) Rain is falling vertically with a speed of 30m/s. A woman rides a bicycle with a speed of 10m/s in the north to south direction. What is the direction in which she should hold her umbrella? A man can swim with a speed of 4Km/h in still water. How long does he take to cross a river 1 km wide if river flows steadily at 3 km/h and he makes his strokes normal to the river current? Also, find the distance covered by him down the river flow. 3 What is the difference in writing a length as 3.2cm and 3.200cm? Find the value of 60 W on a system having 100 g, 20 cm and 1 minute as the fundamental units. 3

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b)

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a) b)

7.

Draw v - t graph for uniformly accelerated motion in the following cases: a) u= +ve , a = + ve b) u= –ve , a = +ve c) u= +ve , a = –ve

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8.

Show that for a projectile fired at an angle of elevation q , there are two times for which the projectile travels the same vertical distance. Also, prove that the sum of the two...