## 27 August 2012

### 9th Force and Laws of Motion - Assignments and Worksheet Term-1

 9th  Force and Laws of Motion - Assignments and  Worksheet Term-1 I Multiple Choice Questions: i) The law of motion given by Newton which gives the definition of force is : a) 1st law b) 2nd law  c) 3rd law d) none of these ii) Inertia of a body is: a) Directly proportional to its mass b) Inversely proportional to mass c) Independent of its mass d) none of these iii) The physical quantity which is a product of mass and velocity of a body is known as: a) Inertia b) Momentum c) Force d) Change in momentum. iv) Action and reaction are equal and opposite and they act on: a) Same bodies b) Different bodies  c) Both a and b d) None v) A gun recoils after firing to conserve: a) Velocity b) Momentum c) Force d) Speed II Give one word for the following. i) Law stating action and reaction are equal and opposite ii) Tendency of a body to oppose any change in its state of rest or uniform motion. iii) The quantity of motion possessed by a moving body. iv) Product of mass and acceleration. v) Physical quantity which causes or tends to cause motion in an object at rest or changes or tends to change the direction of motion of a moving object or the shape or size of the object. III Answer the following questions. i) In the following example, try to identify the number of times the velocity of the ball changes.”A football player kicks a football to another player of his team who kicks the ball towards the goal .The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team.” Also identify the agent supplying the force in each case. ii) It is difficult to balance our body to balance our body when we accidently step on a peel of banana. Explain why. iii) An object of mass 100kg is accelerated uniformly from a velocity of 5m/s to 8m/s in 6 seconds. Calculate the initial and final momentum of the object. Also; find the magnitude of the force exerted on the object? iv) Explain why a gun recoils after firing a bullet. v) Why do we fall in a forward direction when a moving bus brakes to a stop and fall backwards when it accelerates from rest? IV High Order Thinking Questions. i) The force of friction between the surface of a floor and the surface of a box in contact with the floor is 200N. We wish to move the box on the floor with constant velocity. How much force has to be applied on the box? ii) A force of 100N acts on a body moving with a constant velocity of 20m/s on the floor in a straight line. What is the force of friction between the floor and the body? Give reasons for your answer? V Project Work. Take a big rubber balloon and inflate it fully. Tie its neck with a thread. Also using adhesive tape. fix a straw on the surface of the balloon. Pass a thread through the straw and hold one end of the thread in your hand or fix it on the wall .Fix the other end of the thread into another wall at some distance. Now remove the thread tied onto the neck of the balloon. Let the air escape from the mouth of the balloon. In which direction will the straw move. Explain why will that happen?