A train is travelling at a speed of 90 km h-1. Brakes are applied so as to produce a uniform acceleration of – 0.5 m s-2. Find how far the train will go before it is brought to rest.
Initial speed of the train, u = 90 km/h = 90 x 1000 / 60 x 60 = 25 m/s
Final speed of the train, v = 0
Acceleration = −0.5 m s-2
Using equation of motion:
v2 = u2 + 2 as
(0)2 = (25)2 + 2 (−0.5) s
0 = 625 - s
s = 625 m
Where, s is the distance covered by the train
The train will cover a distance of 625 m before it comes to rest.
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Fig. 8.11
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(b) Are all three ever at the same point on the road?
(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
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(iii) the masses of both objects are doubled?
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Fig. 8.12
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Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 40 km h-1. What is the average speed for Abdul’s trip?
How do poriferan animals differ from coelenterate animals?
Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
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Fig 8.11 shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:
Fig. 8.11
(a) Which of the three is travelling the fastest?
(b) Are all three ever at the same point on the road?
(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
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(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled?
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