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What happens to an object when there is no resultant force acting? Newton stated: “Every body continues in a state of rest or uniform motion in a straight line unless acted upon by a resultant force” ______________________ ______________________ ______________________ ______________________ ______________________ ______________________ ______________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ What happens to an object when there is a resultant force? A pupil decides to do an experiment to see how the acceleration of a toy car changed for different resultant forces. This is what the pupil did: 1. Used a long stretched rubber band to accelerate a toy car along a table top. 2. Used a set of light gates to calculate the acceleration of the toy car. 3. Repeated the experiment for 2, 3, 4 and 5 stretched rubber bands. Long Rubber band Toy Car The pupil obtained the following results: 5Resultant Force (N) Acceleration (m/s2) 1 0.25 2 0.5 4- 3- 3 0.75 4 1.0 5 1.25 2- 1- 00 0.25 0.5 0.75 Acceleration m/s2 1.0 1.25 Can you plot the results and make a conclusion about the pupil’s findings. _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ Newton’s second law can be written in word equation form as follows: Resultant Force (N) = Mass (kg) x acceleration (m/s2) Using symbols: F=mxa Note: Only the value for the resultant force can be used in this equation, if the resultant force is zero then the acceleration will also be zero. (Back to Newton’s first law again!) F 1. What resultant force produces an acceleration of 5 m/s2 on a car of mass 0.2 kg? ______________________________________ ______________________________________ ______________________________________ 2. What would be the mass of a spacecraft that developed an acceleration of 20 m/s2 when acted upon by a resultant force of 60,000 N? ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ 3. A sports car of mass 500 kg accelerates steadily due to a 2000N resultant force. Calculate the acceleration of the car. ___________________________________________ ___________________________________________ ___________________________________________ ___________________________________________ ___________________________________________ 4. (a) A mass of 8 kg is accelerated at 5 m/s2 . What resultant force is acting on the mass? _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ (b) If the mass is doubled what resultant force is required to produce the same acceleration? _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 5. (a) What is the acceleration of a mass of 24 kg when a force of 6 N acts on it? _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ (b) What would be the acceleration if the twice the force acted on an object with half the mass? _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 6N 1. When a force of 6 N is applied to a block of mass 2 kg, it moves with a constant velocity along a table. (a) What is the size of the force of friction acting on the block? _______________________________________________________________ (b) Explain how you worked this out? _________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ (c) The driving force is suddenly increased to 10 N, what is the resultant force acting at this instant? _______________________________________________________________ _______________________________________________________________ (d) Calculate the acceleration of the block when the new force is suddenly applied. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 2. A rocket has a mass of 50,000 kg at take off. When the engines first ignite the thrust produced is 1,000,000 N. (a) Calculate the weight of the rocket. _____________________________________ _____________________________________ _____________________________________ _____________________________________ (b) Draw the two forces acting on the rocket at take-off. (c) Calculate the resultant force acting on the rocket. _______________________________________________________________ _______________________________________________________________ (c) Calculate the initial acceleration of the rocket at take-off. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ (d) As the rocket speeds up another force acts on the rocket. Name this force and explain how this force is produced. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 3. A speed boat has a mass of 3000kg. The engines produce a thrust of 5000N and the water resistance is 1000N. 3000kg mass of speed boat 5000N 1000N (a) Calculate the resultant force acting on the boat. __________________________________________________________ __________________________________________________________ (b) Calculate the acceleration of the boat. __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ (c) Explain what happens to the water resistive force as the boat speeds up. __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ 1. In the following examples decide whether the forces on the moving object balanced or unbalanced? (a) A car maintaining a constant speed along a straight road. _____________________________________________________________ [1] (b) A train braking as it approaches a station. _____________________________________________________________ [1] (c) A rocket during take-off. _______________________________________ [1] (d) A pupil sitting on a stool. ______________________________________ [1] 2. Calculate the resultant force on each car in the following diagrams. 100N 20N 950N 35N 150N ________________ ________________ ________________ _____________ [1] 250N ________________ ________________ ________________ ______________[1] ________________ ________________ ________________ ______________[1] 3. A bike and its rider have a total mass of 95kg. (a)Calculate the acceleration if the rider can produce a resultant force of 250N. _______________________________________ _______________________________________ _______________________________________ _____________________________________ [2] (b) Why do cyclists crouch down over the handlebars when they want to go faster? _______________________________________________________________ _______________________________________________________________ _____________________________________________________________ [1] 4. A family car has a total mass of 1500kg. 3500N 250N It produces a driving force of 3500N in order to start moving. The friction force is 250N. (a) Calculate the resultant force acting on the car. __________________________________________________________ ________________________________________________________ [1] (b) Calculate the acceleration as it starts to move. __________________________________________________________ __________________________________________________________ __________________________________________________________ ________________________________________________________ [2] 5. For each of the following objects calculate: (a) Its weight (b) The resultant force acting (c) The acceleration 10N 50N 20N 4kg 10kg 2kg Weight Weight Weight __________________ __________________ __________________ __________________ __________________ __________________ __________________ __________________ __________________ ________________ [4] __________________ __________________ __________________ __________________ __________________ __________________ __________________ __________________ __________________ ________________ [4] __________________ __________________ __________________ __________________ __________________ __________________ __________________ __________________ __________________ ________________ [4] 6. A rocket has a mass of 10,000kg. The thrusters produce a thrust force of 400,000N and air resistance just after take-off is 500N. (a) Calculate the weight of the rocket. ___________________________________________ _________________________________________ [1] (b) Find the resultant force on the rocket. ___________________________________________ ___________________________________________ _________________________________________ [2] (c) Calculate the acceleration of the rocket. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _____________________________________________________________ [2] 7. A sailing boat of mass 5000kg experiences a water resistive force of 800N. The wind, helping to push the boat along, provides a force of 2000N. The engines, turning the propeller, also provide a forwards force of 1000N. (a) Draw a diagram of a sailing boat and show the action of these forces. [4] (b) Calculate the resultant force acting on the boat. _______________________________________________________________ ____________________________________________________________ [2] (c) Calculate the acceleration of the boat. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _____________________________________________________________ [2]