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Question

A 1500kg car is moving at a speed of 50ms-1 When brakes are applied it stops with uniform retardation at a distance of 150m. Calculate the force applied by the brakes of the car and the work done before stopping?


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Solution

Step 1: Given data

Mass,m=1500kgInitialvelocity,u=50m/sdisplacement,s=150mFinalvelocity,v=0

Step 2: Find the acceleration

Using the third equation of motion

v2=u2+2as0=502+2×a×150a=-2500300a=(-253)m/s2

Step 3: Find the force

Force,F=maF=1500×(-253)Force=-12500N

Negative force implies the force acting on an object against the applied force.

Step 4: Finding the work done

Workdone,W=F.sW=-12500×150W=-1875×103JW=-1875KJ

Here, the negative sign indicates that the work is done against the displacement.

Hence, the force applied is 12500N and work done is -1875kJ.


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