A car covers $30 k m$ at a uniform speed of $60 k m / h r$ and the next $30 k m$ at a uniform speed of $40 k m / h r$ . The total time taken is

30 m i n

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45 m i n

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75 m i n

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120 m i n

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Solution

The correct option is C $75 m i n$
$t_{1} = \frac{s}{v_{1}} \Rightarrow t_{1} = \frac{30}{60} = \frac{1}{2} h r$
$t_{2} = \frac{s}{v_{2}} \Rightarrow t_{2} = \frac{30}{40} = \frac{3}{4} h r$
$t = t_{1} + t_{2} = (\frac{1}{2} + \frac{3}{4}) h r \Rightarrow t = 75 m i n$

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a) A train travels a distance with a speed of 40 km/h and returns with a speed of 60 km/h. Calculate the average speed of the train.

b) On a 60 km track, a train travels the first 30 km at a uniform speed of 30 km/h. How fast must a train travel the next 30 km so that the average speed is 40 km/hr for the entire trip?

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. The average speed of the car is -

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A car covers 30km at a uniform speed of 60km/hr and the next 30km at a uniform speed of 40km/hr. The total time taken is

The correct option is C 75mint1=sv1⇒t1=3060=12hrt2=sv2⇒t2=3040=34hrt=t1+t2=(12+34)hr⇒t=75min

A car covers $30 k m$ at a uniform speed of $60 k m / h r$ and the next $30 k m$ at a uniform speed of $40 k m / h r$ . The total time taken is

The correct option is C $75 m i n$
$t_{1} = \frac{s}{v_{1}} \Rightarrow t_{1} = \frac{30}{60} = \frac{1}{2} h r$
$t_{2} = \frac{s}{v_{2}} \Rightarrow t_{2} = \frac{30}{40} = \frac{3}{4} h r$
$t = t_{1} + t_{2} = (\frac{1}{2} + \frac{3}{4}) h r \Rightarrow t = 75 m i n$