Question

Find the average frictional force needed to stop a car
weighing 500 kg in a distance of 25 m if the initial speed
is 72 km/h.

Answer 1

This question can be solved more easily using the “Work – Energy Theorem”

We know, Wnet = ΔK.E

∴  ∑F x s = ½ mv2 - ½ mu2

∴ F x 24 = ½ x 500 x 202

∴ F = 4000N






Here we use the third equation of motion. i.e.

here s= 25 m
v= 72 km/hr = 20 m/s
u= 0
so
a= 8 m/s (square)
and hence the force is
F=ma= 4000 N

Answer 2

Answer:

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