Q1. State what will happen to an object under each of the following circumstances:


  1. No resultant force acts on a stationary object.


In this case, of course according to Newton's first law nothing will happen as the object will remain stationary.


  1. A resultant force acts on a stationary object.


The object will start to accelerate in the direction of the resultant force.


  1. No resultant force acts on a moving object.


The object will continue to move in its original direction at the same velocity i.e. there will be no effect.


  1. A resultant force acting on a moving object in the same direction as the object's motion.


The object will accelerate in the direction of its motion as the force acting upon it is also in that direction.


  1. A resultant force acting on a moving object in the opposite direction to the object's motion.


As the resultant force is working in the opposite direction to the object's motion, the object will decelerate (slow down)


Q2. Consider the 5 diagrams A-E of the car shown below. Taking into account the arrows which depict the direction and magnitude of forces acting on the car in each situation, describe what you believe the effect would be on the car in each case.


Driving Force - Thrust

Resistive Force - Drag

Vertical Force - Reactive

Force of Gravity - Weight


A. In the case of vehicle A the driving force (thrust) and resistive force (drag) are equal and opposite. This means that with regard to horizontal movement, the vehicle will be remaining stationary. However, the vertical force (reactive force) is only counteracted in part by the force of gravity pulling the vehicle downwards (vehicle weight) which means that the resultant force would lift the vehicle vertically upwards.


B. In the case of vehicle B the driving force (forward) is greater than the resistive force trying to hold the vehicle back therefore the resultant force would mean that the vehicle would move forwards. In addition to this the vertical force upwards is not completely compensated by the vertical force downwards (force of gravity/acceleration due to gravity) so as mother moving forward the vehicle was start to move upwards, probably towards the 2 o'clock position on a standard clockface.


C. Vehicle C has equal and opposite driving and resistive forces and so the resultant here would mean that the vehicle (as far as forwards/backwards is concerned) would stay still, however the force pulling the vehicle downwards and forces pulling the vehicle upwards are also in balance so the vehicle would not move at all in any direction.


D. The 4th vehicle, vehicle D has a driving force to the right which is in excess of the resistive force to the left and so the resultant force on the vehicle would push it to the right (forwards). In addition to this the force of gravity/acceleration due to gravity (downward force) is greater than the upthrust force, which would mean that as well as moving forwards (to the right) the vehicle tried to move downwards, with a possible overall result of moving approximately to the 4 o'clock/5 o'clock position on a standard clockface.


E. The final vehicle, vehicle E shows pairs of forces that would move the vehicle approximately in the direction at 10 o'clock/11 o'clock on a standard clockface. The horizontal resultant force would pull the vehicle backwards (to the left) and the vertical resultant force would attempt to move the vehicle vertically upwards, the overall result being approximately as stated previously.



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