The bullet from a rifle travels at a speed of 3*10^4 cm/s.Work out the length of time in seconds taken for the bullet to hit a target 54m away. 

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changchengliang's profile pic

changchengliang | Elementary School Teacher | (Level 2) Adjunct Educator

Posted on

Let's go back to our basics.  The formula for distance is given by:

Distance = speed x time

Rearranging, we have:

Time = Distance/speed

Let's work in cm

1m = 100cm


So,

54m = 5400cm

Substituting this value (in cm) into the formula for time, we have:

Time

=  5400 / speed

=  5400 / 30000

0.18 (secs)

The bullet will take 0.18 sec [that's about 1/5 of a second!] to reach its target.
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A gentle note:

Be very careful with what units you are using.  Speed can be in km/h, m/s, cm/s etc.  Substituting the wrong values for the formula can have grave consequences.

neela's profile pic

neela | High School Teacher | (Level 3) Valedictorian

Posted on

The distance of the terget = 54meter.

Speed of the bullet = 3*10^4cm

Time taken to by the bullet =  distance of the target /speed of the bullet. But here the speed of the bullet is given in centimeter per second. So we have to convert this into meter/second  as the distance is in meter. For this we have to multiply the speed of the bullet by 0.01.

 Therefore the speed of the bullet in m/s = 3*10^4*0.01 = 3*10^2 m/s.

Therefore the time taken by the bullet to reach the target = 54/3*10^2 s  = 0.18 seconds.

Therefore the bullet takes 0.18 seconds to reacg the target.

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