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Motion | A scooterist covers a distance of 3 kilometres in 5 minutes. Calculate his speed in:

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 Class 9 Motion Physics

1. A scooterist covers a distance of 3 kilometres in 5 minutes. Calculate his speed in:
(a) centimetres per second (cm/s)
(b) metres per second (m/s)
(c) kilometres per hour (km/h)

Solution. (a) In order to calculate the speed in centimetres per second we should convert the given distance of 3 kilometres into centimetres and the given time of 5 minutes into seconds. Please note that 1 kilometre has 1000 metres and 1 metre has 100 centimetres. Now,

Distance travelled =3 km

 = 3 x 1000 m

= 3 x 1000 x100 cm

= 300,000 cm ----------------- (1)

Time taken = 5 minutes

= 5 x 60 seconds

 = 300 s ------------------------------ (2)

 

 We know that,

Speed = Distance travelled / Time taken

=  300,000 cm  / 300 s

= 1000 cm/s --------------- (3)

 Thus, the speed of scooterist is 1000 centimetres per second.

(b) In order to express the speed in metres per second we should convert the given distance of 3 kilometres into metres and the given time of 5 minutes into seconds. Thus, in this case:

Distance travelled =3 km

=3 x 1000 m

= 3000 ---------------------- (4)

 

Time taken = 5 minutes

= 5 x 60 seconds

= 300 s ------------------------(5)

Now,  Speed = Distance travelled / Time taken

= 3000 m 300 s

=10 m/s ---------------------- (6)

So, the speed of scooterist is 10 metres per second.

 

(c) And finally, in order to calculate the speed in kilometres per hour, we should express the given distance in kilometres (which is already so), and the given time in hours. So, in this case

Distance travelled = 3 km ----------  (7)

 Time taken = 5 minutes

= 5 hours / 60 hours

= 0.083 h -----------------------------(8)

We know that,      Speed = Distance travelled / Time taken

= 3 km / 0.083 h

 = 36 km/h ---------------------------------- (9)

Thus, the speed of scooterist is 36 kilometres per hour.

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