# Physics Questions Answers

11) A train, 800 meter long is running with a speed of 78 km/hr. It crosses a tunnel in 1 minute. What is the length of the tunne

- 1) 650 meter
- 2) 555 meter
- 3) 500 meter
- 4) 458 meter

**Ans.**C

**Explanation :**

Let length of tunnel is x meter Distance = 800+x meter Time = 1 minute = 60 seconds Speed = 78 km/hr = 78*5/18 m/s = 65/3 m/s Distance = Speed*Time \begin{aligned} => 800+x = \frac{65}{3}*60 \=> 800+x = 20*65 = 1300 \=> x = 1300 - 800 = 500 \\end{aligned} So the length of the tunnel is 500 meters. [If you want to calculate it practically, then please have your copy and pen and take a ride of Kalka to Shimla toy train in north India. It has many tunnels on the way :) ]

12) A jogger running at 9 kmph alongside a railway track is 240 metres ahead of the engine of a 120 metre long train running at 45 kmph in the same direction. In how much time will the train pass the jogger

- 1) 30 seconds
- 2) 32 seconds
- 3) 34 seconds
- 4) 36 seconds

**Ans.**D

**Explanation :**

Speed of train relative to jogger = (45-9) = 36 kmph = 36*(5/18) = 10 m/sec Distance to cover = 240 + 120 = 360 metres Time = Distance/Speed So, \begin{align} Time = \frac{360}{10} = 36 \text{ Seconds} \end{align}

13) A train overtakes two persons who are walking in the same direction in which the train is going, at the rate of 2 kmph and 4 kmph and passes them completely in 9 and 10 seconds respectively. Find the length of trai

- 1) 45 m
- 2) 50 m
- 3) 55 m
- 4) 60 m

**Ans.**B

**Explanation :**

First person speed = 2*(5/18) = 5/9 m/sec Second person speed = 4*(5/18) = 10/9 m/sec Let the length of train is x metre and speed is y m/sec then, \begin{aligned} \frac{x}{y-\frac{5}{9}} = 9 \=> 9y-5 = x \=> 9y-x = 5 .....(i) \Also, \\frac{x}{y-\frac{10}{9}} = 10 \90y-9x = 100 .....(ii)\ \text{from (i) and (ii), we get,} \x=50 \end{aligned} So length of train is 50 metre

14) Two trains 140 metre and 160 metre long run at the speed of 60 km/hr and 40 km/hr respectively in opposite direction on parallel tracks. What time these will take to cross each other

- 1) 10.7 Seconds
- 2) 10.8 Seconds
- 3) 10.9 Seconds
- 4) 11.8 Seconds

**Ans.**B

**Explanation :**

Relative Speed = 60+40 = 100 Kmph = 100*(5/18) = 250/9 m/sec Distance to be covered = 140 + 160 = 300 metres Time = Distance/Speed \begin{aligned} Time = 300*\frac{9}{250} \= \frac{54}{5} = 10.8\text{ seconds} \end{aligned}

15) Two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively and they cross each other in 23 seconds. The ratio of their speeds i

- 1) 1:3
- 2) 3:2
- 3) 3:5
- 4) 3:7

**Ans.**B

**Explanation :**

Let the speeds of the two trains be x m/sec and y m/sec respectively. Then, length of the first train = 27x metres, Length of the second train = 17y metres. [because distance = speed*time] \begin{aligned} \frac{27x+17y}{x+y} = 23 \=> 27x + 17y = 23x + 23y \=> 4x = 6y \=> \frac{x}{y} = \frac{6}{4} \end{aligned} So ratio of the speeds of train is 3:2

16) A 300 meter long train crosses a platform in 39 seconds while it crosses a signal pole in 18 seconds. What is the length of the platfor

- 1) 310 meter
- 2) 335 meter
- 3) 345 meter
- 4) 350 meter

**Ans.**D

**Explanation :**

Speed = Distance/time = 300/18 = 50/3 m/sec Let the length of the platform be x meters then \begin{aligned} Distance = Speed*Time \x+300 = \frac{50}{3}*39 \=>3(x+300)= 1950 \=> x = 350 \text{ meters} \end{aligned}

17) A train speeds past a pole in 15 seconds and a platform 100 meter long in 25 seconds. What is length of the trai

- 1) 140 meter
- 2) 145 meter
- 3) 150 meter
- 4) 155 meter

**Ans.**C

**Explanation :**

Let the length of the train is x meter and Speed of the train is y meter/second Then x/y = 15 [because distance/speed = time] => y = 15/x \begin{aligned} => \frac{x+100}{25} = \frac{x}{15} \x = 150 \text{ meters} \end{aligned} So length of the train is 150 meters

18) Speed of a goods train is 72 km/hr. This train crosses a 250 meter platform in 26 seconds. Then find the length of goods trai

- 1) 250 meters
- 2) 260 meters
- 3) 270 meters
- 4) 280 meters

**Ans.**C

**Explanation :**

First convert speed from km/hr to m/sec So, Speed = 72*(5/18) = 20 m/sec Time = 26 seconds Let the length of the train be x meters. We know, Distance = Speed*Time. [you can remember this formula as remembering DUST = D*ST... Distance=Speed*Time] x+250 = 20*26 => x = 270 meters So length of the goods train is 270 meter

19) Two trains of equal length are running on parallel lines in the same direction at 46 km/hr and 36 km/hr. The faster train passes the slower train in 36 seconds. The length of each train i

- 1) 40 meter
- 2) 45 meter
- 3) 50 meter
- 4) 55 meter

**Ans.**C

**Explanation :**

Let the length of each train is x meter Distance will be x+x = 2x Relative Speed = 46-36 = 10 km/hr = 10*(5/18) = 25/9 m/sec Distance = Speed*Time \begin{aligned} 2x = \frac{25}{9}*36 \2x = 100 \=> x = 50 \end{aligned} So length of both the trains are 50 meters

20) A 270 metres long train running at the speed of 120 kmph crosses another train running in opposite direction at the speed of 80 kmph in 9 seconds. What is the length of the other tra

- 1) 220 meter
- 2) 225 meter
- 3) 230 meter
- 4) 235 meter

**Ans.**C

**Explanation :**

As trains are running in opposite directions so their relative speed will get added So, Relative speed = 120 +80 = 200 kmph = 200*(5/18) = 500/9 m/sec Let the length of other train is x meter then \begin{aligned} \frac{x+270}{9} = \frac{500}{9} \ => x+270 = 500\ => x = 230 \end{aligned} So the length of the train is 230 meters