# Question

This question is about projectile motion and the use of an energy argument to find the speed with which a thrown stone lands in the sea.

Christina stands close to the edge of a vertical cliff and throws a stone. The diagram below* (not drawn to scale)* shows part of the trajectory of the stone. Air resistance is negligible.

Point P on the diagram is the highest point reached by the stone and point Q is at the same height above sea level as point O.

(a) At point P on the diagram above draw arrows to represent

(i) the acceleration of the stone (label this A).

(1)

(ii) the velocity of the stone (label this V).

(1)

The stone leaves Christina’s hand (point O) at a speed of 15 m s−1 in the direction shown. Her hand is at a height of 25 m above sea level. The mass of the stone is 160 g. The acceleration due to gravity *g* = 10 m s−2.

(b) (i) Calculate the kinetic energy of the stone immediately after it leaves Christina’s hand.

...........................................................................................................................

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(1)

(ii) State the value of the kinetic energy at point Q.

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(1)

(iii) Calculate the loss in potential energy of the stone in falling from point Q to hitting the sea.

(1)

(iv) Determine the speed with which the stone hits the sea.

(2)

(Total 7 marks# Answer

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