3.       This question is about collisions.

(a)     State the principle of conservation of momentum.

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(b)     In an experiment, an air-rifle pellet is fired into a block of modelling clay that rests on a table.

(not to scale)

          The air-rifle pellet remains inside the clay block after the impact.

          As a result of the collision, the clay block slides along the table in a straight line and comes to rest. Further data relating to the experiment are given below.

                   Mass of air-rifle pellet                       = 2.0 g
Mass of clay block                            = 56 g
Velocity of impact of air-rifle pellet    = 140 m s–1
Stopping distance of clay block          = 2.8 m

(i)      Show that the initial speed of the clay block after the air-rifle pellet strikes it is
4.8 m s–1.

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(ii)     Calculate the average frictional force that the surface of the table exerts on the clay block whilst the clay block is moving.

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(c)     Discuss the energy transformations that occur in the clay block and the air-rifle pellet from the moment the air-rifle pellet strikes the block until the clay block comes to rest.

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(d)     The clay block is dropped from rest from the edge of the table and falls vertically to the ground. The table is 0.85 m above the ground. Calculate the speed with which the clay block strikes the ground.