66. A car goes 20 metres in a second. Find its speed in km/hr.

1. 1. 18

   
   
   

   2. 72

   
   
   

   3. 36

   
   
   

   4. 20

   
   
   

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1. View Hint View Answer Discuss in Forum

   1 m/sec =	18	kmph
   	5

   
   

   ∴  20 m/sec =	20 × 18	= 72 kmph
   	5

   Correct Option: B

   1 m/sec =	18	kmph
   	5

   
   

   ∴  20 m/sec =	20 × 18	= 72 kmph
   	5

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67. The speed of a car is 54 km/hr. What is its speed in m/sec?

1. 1. 15 m/sec

   
   
   

   2. 19-44 m/sec

   
   
   

   3. 194.4 m/sec

   
   
   

   4. 150 m/sec

   
   
   

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1. View Hint View Answer Discuss in Forum

   1 kmph =	5	m/sec
   	18

   
   

   ∴  54 kmph =	5	× 54
   	18

   
   = 15 m/sec.

   Correct Option: A

   1 kmph =	5	m/sec
   	18

   
   

   ∴  54 kmph =	5	× 54
   	18

   
   = 15 m/sec.

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68. A car covers a certain distance in 25 hours.

    If it reduces the speed by	1	th,the car covers 200 km.
    	5

    less in that time. The speed of car is

1. 1. 60 km./hr.

   
   
   

   2. 30 km./hr.

   
   
   

   3. 40 km./hr.

   
   
   

   4. 50 km./hr.

   
   
   

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1. View Hint View Answer Discuss in Forum

   Speed of car = x kmph.
   ∴  Distance = Speed × Time
   = 25x km.
   Case II,
   

   Speed of car =	4x	kmph.
   	5

   
   

   Distance covered =	4x	× 25
   	5

   
   = 20x km.
   According to the question,
   25x – 20x = 200
   ⇒  5x = 200
   

   ⇒  x =	200	= 40 kmph.
   	5

   Correct Option: C

   Speed of car = x kmph.
   ∴  Distance = Speed × Time
   = 25x km.
   Case II,
   

   Speed of car =	4x	kmph.
   	5

   
   

   Distance covered =	4x	× 25
   	5

   
   = 20x km.
   According to the question,
   25x – 20x = 200
   ⇒  5x = 200
   

   ⇒  x =	200	= 40 kmph.
   	5

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69. A car moving in the morning fog passes a man walking at 4 km/h. in the same direction. The man can see the car for 3 minutes and visibility is upto a distance of 130 m. The speed of the car is :

1. 1. 7	3	km. per hour
      	5

   
   
   

   2. 6	3	km. per hour
      	5

   
   
   

   3. 7 km. per hour

   
   
   

   4. 5 km. per hour

   
   
   

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1. View Hint View Answer Discuss in Forum

   Speed of car = x kmph.
   Relative speed = (x – 4) kmph.
   

   Time = 3 minutes =	3	hours =	1	hours
   	60		20

   
   Distance = 130 metre
   

   =	130	km. =	13	km.
   	1000		100

   
   

   ∴  Relative speed =	Distance
   	Time

   
   

   ⇒  x – 4 =	13	× 20
   	100

   
   ⇒  5x – 20 = 13
   ⇒  5x = 20 + 13 = 33
   

   ⇒  x =	33	= 6	3	kmph.
   	5		5

   Correct Option: B

   Speed of car = x kmph.
   Relative speed = (x – 4) kmph.
   

   Time = 3 minutes =	3	hours =	1	hours
   	60		20

   
   Distance = 130 metre
   

   =	130	km. =	13	km.
   	1000		100

   
   

   ∴  Relative speed =	Distance
   	Time

   
   

   ⇒  x – 4 =	13	× 20
   	100

   
   ⇒  5x – 20 = 13
   ⇒  5x = 20 + 13 = 33
   

   ⇒  x =	33	= 6	3	kmph.
   	5		5

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70. A boy rides his bicycle 10km at an average speed of 12 km/hr and again travels 12 km at an average speed of 10 km/hr. His average speed for the entire trip is approximately :

1. 1. 10.4 km/hr

   
   
   

   2. 10.8 km/hr

   
   
   

   3. 11.0 km/hr

   
   
   

   4. 12.2 km/hr

   
   
   

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1. View Hint View Answer Discuss in Forum

   Total distance = 10 + 12 = 22 km
   

   Total time =	10	+	12
   	12		10

   
   

   =	244	hours
   	120

   
   

   ∴  Required average speed =	Total distance
   	Total time

   
   

   =	22
   	244
   	120

   
   

   =	22	× 120 = 10.8 km/hr.
   	244

   
   
   Second Method :
   Here, d₁ = 10, S₁ = 12
   d₂ = 12, S₂ = 10
   

   Average Speed =	d1 + d2
   	d1	+	d2
   	S1		S2

   
   

   =	10 + 12
   	10	+	12
   	12		10

   
   

   =	22 × 120	= 10.8 km/hrs.
   	244

   Correct Option: B

   Total distance = 10 + 12 = 22 km
   

   Total time =	10	+	12
   	12		10

   
   

   =	244	hours
   	120

   
   

   ∴  Required average speed =	Total distance
   	Total time

   
   

   =	22
   	244
   	120

   
   

   =	22	× 120 = 10.8 km/hr.
   	244

   
   
   Second Method :
   Here, d₁ = 10, S₁ = 12
   d₂ = 12, S₂ = 10
   

   Average Speed =	d1 + d2
   	d1	+	d2
   	S1		S2

   
   

   =	10 + 12
   	10	+	12
   	12		10

   
   

   =	22 × 120	= 10.8 km/hrs.
   	244

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