A tennis ball, moving horizontally, hits a wall at \(25 \mathrm {~ms} ^ { - 1 }\) and rebounds along the same straight line at \(15 \mathrm {~ms} ^ { - 1 }\). The impulse exerted by the wall on the ball has magnitude 12 Ns .
- Calculate the mass of the ball.
- State any modelling assumptions that you have made.
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Forces of magnitude \(4 \mathrm {~N} , 5 \mathrm {~N}\) and 8 N act on a particle in directions whose bearings are \(000 ^ { \circ } , 090 ^ { \circ }\) and \(210 ^ { \circ }\) respectively. Find the magnitude of the resultant force and the bearing of the direction in which it acts.