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A man on a bike of total mass 100 kg, is free-wheeling at a constant speed...

A man on a bike of total mass 100 kg, is free-wheeling at a constant speed of 15 ms-1 down a hill with a gradient of 10%. He wants to slow down to a safer speed, so he applies the brake lightly to produce a constant braking force of 84 N. The air resistance is proportional to the square of the speed.

(a) Calculate the deceleration when his speed has dropped to 12 ms-1.

(b) At what speed will his deceleration be reduced to zero?

(c) Draw a sketch of the (t v) graph for the motion.

Answers: (a) 0.48 ms-2 (b) 6 ms-1

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