SATHEE: Kinematics Question 370

Kinematics Question 370

Question: A metro train starts from rest and in 5 s achieves 108 km/h. After that it moves with constant velocity and comes to rest after travelling 45 m with uniform retardation. If total distance travelled is 395 m, find total time of travelling.

Options:

A) 12.2s

B) 15.3s

C) 9s

D) 17.2s

Show Answer

Answer:

Correct Answer: D

Solution:

Given: $u = 0,$

$t = 5 s e c,$

$v = 108 k m / h r$

$= 30 m / s$ By equation of motion $v = u + a t$

$or a= \frac{v}{t} = \frac{30}{5} 6 m/ s^{2} [∴ u = 0]$

$S_{1} = \frac{1}{2} a t^{2} = \frac{1}{2} \times 6 \times 5^{2} = 75 m$

distance travelled in first 5 sec is 75m. distance travelled with uniform speed of 30 m/s it’s $S_{2}$

$395 = S_{1} + S_{2} + S_{3} \Rightarrow 395 = 75 + S_{2} + 45$
$\Rightarrow S_{2} = 275 m$

Time taken to travel $275 m = \frac{275}{30} = 9 .2 sec$ For retarding motion, we have $0^{2} - 30^{2} = 2 (- a) \times 45, we get a = 10 m/ s^{2}$

$S = u t + \frac{1}{2} a t^{2} \Rightarrow 45 = 30 t + \frac{1}{2} (- 10) t^{2}$
$\Rightarrow 45 = 30 t - 5 t^{2}$

On solving we get, $t = 3 s e c$ Total time taken $= 5 + 9.2 + 3 = 17.2 s e c .$

Kinematics Question 370

Question: A metro train starts from rest and in 5 s achieves 108 km/h. After that it moves with constant velocity and comes to rest after travelling 45 m with uniform retardation. If total distance travelled is 395 m, find total time of travelling.

Options:

Answer:

Solution:

Engineering Preparation

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NCERT Books & Solutions

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Sample Mock Test

Mentorship

NCERT Exercise Video Solution

Kinematics Question 370

Question: A metro train starts from rest and in 5 s achieves 108 km/h. After that it moves with constant velocity and comes to rest after travelling 45 m with uniform retardation. If total distance travelled is 395 m, find total time of travelling.

Options:

Answer:

Solution:

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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