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CBSE Class 9 Answered

A car of mass 1000 kg is moving with a certain speed when a constant braking force of 1000 N acts on it for 5 seconds and the speed of the car reduces to half its original speed. Find the further time required to stop the car if the same braking force acts.
Asked by rachitraj152007 | 03 Jan, 2021, 07:10: PM
Expert Answer
Retardation = breaking force / mass = 1000 N/ 1000 kg = 1 m/s2 
 
Let us use the following equation of motion to get intial speed u from known retardation a
 
v = u - (a × t ) ...................(1)
 
where u is initial speed,  v is speed after t seconds and a is retardation. 
 
Since after 5 seconds , speed is reduced to half, then we have
 
( u/2 ) = u - ( 1 × 5 )   or  we get  initial speed u = 10 m/s
 
speed after 5 seconds = (10 / 2 ) = 5 m/s
 
time require to stop completely is determined from eqn.(1) by substituting final speed v = 0 and initial speed u = 5 m/s
 
0 = 5 - (1 × t )   or  time to stop the vehicle , t = 5 s
Answered by Thiyagarajan K | 03 Jan, 2021, 07:31: PM

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