Question

please tell me 4th and 5th question in detail

Answer 1

4) Let the train accelerates from 0 to v at a rate A in time t1. Let the distance traveled in this time be S1

A = v-0/t1

t1 = v/A

S1 = 0 + 1/2 At^$2_{1}$ = v2/2A

Then it moves with constant speed v for time t2. Let the distance traveled in this time be S2

S2 = vt2

It then decelerates from V to 0 at rate B in time t3. Let the distance traveled in this time be S3

t3 = v/B

now using,
v2 = u2 + 2as

= 0 = v2 - 2BS3

= S3 = v2 / 2B

Given Total distance covered is L
 L = S1 + S2 + S3

=  L = v2/2A + v$t_{2}$ + v2/2B

= $t_{2}$ = L/v - v/2A - v/2B

now total time taken is 
t1+ t2 + t3

= v/A + L/v - v/2A - v/2B + v/B
= L/v + v/2A + v/2B
= L/v + v/2 (1/A + 1/B)

5) use v2 = u2 +- 2as
for v2 = 2a1s1 also v2 = 2a2s2

1/a1 = 2s1/v2 - (a)

1/a2 = 2s2/v2 - (b)

v = a1t1 - (1)

v = a2t2 (2)

and t1 + t2 = 240 (3)

solve these equations to find 1/a +1/a ...