Plz answer these questions
A train is travelling at a speed of 90 km hr -1 . Brakes are applied so as to produce a uniform
acceleration of -0.5ms -2 . Find how far the train will go before it is brought to rest.
2. Find the initial velocity of a car that is stopped in 10 s by applying brakes. Retardation due to
brakes is 2.5ms -2 .
3. A trolley while going down on an inclined plane has an acceleration of 2cms -2 . What will be its
velocity 3 s after start?
4. A motorboat starting from rest on a lake accelerates in a straight line at a constant rate of3 ms -2 for
8 s. How far does the boat travel during this time?
Answers
Answer:
1) given u = 90km/h = 5×90/18 = 25m/s, acc = -0.5m/s^2
its final velocity(v) = 0 , s = ?
by second equation of motion ,
v^2 - u^2 = 2as
0^2 - (25)^2 = 2(-0.5)(s)
=> s = 625m
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2) retardation is nothing deceleration
a = - 2.5m/s^2 , time = 10sec, final velocity = 0
by first equation of motion ,
v = u + at
where v is final velocity , u is initial velocity , a is acc , t is time
0 = u + (-2.5)(10)
-u = -25
=> u = 25m/s
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3) t = 3sec , a= 2cm/s^2 = 0.02m/s^2 , u = 0
by first equation of motion ,
v = u + at
v = 0.02(3) + 0
v = 0.06m/s
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4) u =0 (∵ it has started from rest ) , a = 3m/s^2 , t = 8sec ,
s = ?
by third equation of motion ,
s = ut + at^2/2
s = 0(8) + 3(64)/2
s = 0 + 32(3)
=> s = 96m