A 70 kg base runner begins his slide into second base when he is moving at a spe

Question

A 70 kg base runner begins his slide into second base when he is moving at a speed of 4 m/s. The coefficient of friction between his clothes and Earth is 0.70. He slides so that his speed is zero just as he reaches the base. How much mechanical energy is lost due to friction acting on the runner? How far does he slide? An automobile having a mass of 1000 kg is driven into a brick wall in a safety test. The bumper behaves like a spring with a constant 5.00 times 10^5 N/m and is compressed 3.06 cm as the car is brought to rest. What was the speed of the car before the impact assuming no energy is lost in the collision with the wall?

Explanation / Answer

Problem 9:

Given,

Mass of runner, m = 70 kg

Velocity, v = 4 m/s

Coefficient of friction, = 0.70

a) Kinetic energy, KE = 0.5 mv² = 0.5 x 70 x 4.0 = 560 J

b) Work (W) = force (F) × distance (d)

The frictional force, F = mg = 0.70 x 9.81 x 70 = 480.7 N

KE = F x d, so d = KE/F

Distance, d = 560 J / 480.7 N = 1.16 m

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