State Newton's third law of motion.

1. (a)State Newton's third law of motion.[2]
2. (b)A block X of mass mx slides in a straight line along a horizontal frictionless surface, as shown in Fig. 3.1. [Figure 3.1] The block X, moving with speed 5v, collides head-on with a stationary block Y of mass mү. The two blocks stick together and then move with common speed v, as shown in Fig. 3.2. [Figure 3.2]
3. (b)(i)Use conservation of momentum to show that the ratio mү / mx is equal to 4.[2]
4. (b)(ii)Calculate the ratio total kinetic energy of X and Y after collision / total kinetic energy of X and Y before collision ratio =[3]
5. (b)(iii)State the value of the ratio in (ii) for a perfectly elastic collision. ratio[1]
6. (c)The variation with time t of the momentum of block X in (b) is shown in Fig. 3.3. [Figure 3.3] Block X makes contact with block Y at time t = 20 ms.
7. (c)(i)Describe, qualitatively, the magnitude and direction of the resultant force, if any, acting on block X in the time interval: 1. t = 0 to t = 20 ms 2. t = 20 ms to t = 40 ms.[3]
8. (c)(ii)On Fig. 3.3, sketch the variation of the momentum of block Y with time t from t = 0 to t = 60 ms.[3]

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