Q19 · 2020 · Technology-activeComplex unfamiliar7 marks
QUESTION 19 (7 marks)
An object is swinging at the end of a 0.5 m length of string in a vertical circular path with a constant angular speed, completing each revolution in 0.24 seconds. The object is projected from a height of 0.3 m above the ground in a vertical plane and just passes over a narrow pole as shown in the diagram. The pole is 2.05 m high and its base is 14 m horizontally from where the object was projected. A flat-topped vehicle of length 0.6 m and height 0.4 m is initially at rest against the pole as shown. At the instant that the object is projected, the vehicle moves in a horizontal direction away from the pole in the same vertical plane with an acceleration of magnitude m s. The object strikes the middle of the top of the vehicle. Assuming that air resistance is negligible, use vector calculus to model the motion of the projectile in the vertical plane and determine .
WORKED SOLUTION
7 marksQCAA guide · typeset solution
ANSWER
m s.
Worked solution
The angular speed is , so the release speed is m s. Modelling the projectile gives and . The point lies on the path, giving . Setting gives the relevant impact position m and time s. The vehicle centre starts at m, so , hence m s.
correctly determines the tangential velocity of object
identifies the parametric form of the projectile path
determines the Cartesian form of the projectile path
determines the angle of release of the object
determines the horizontal displacement at impact
determines the time of flight
determines the acceleration of the trolley
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