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How do I solve the following problem? Could someone please provide an explanation instead of giving me a number? Thanks.

A boy on a bicycle is pedaling along a straight and level road at 26.30 km/hr. When he stops pedaling he finds that he can travel a distance of 150 meters before stopping. Find

a. his speed in m/sec when he stops pedaling
b. his acceleration while coasting
c. the coefficient of sliding friction

2007-11-10 06:26:06 · 1 answers · asked by labelapark 6 in Science & Mathematics Physics

1 answers

a) By the givens in the question, the bike was doing 26.3 kph; so all you need to do is change the units remembering 1 km = 1,000 m and 1 hr = 60 sec/min X 60 min = 3600 seconds

b) v^2 = u^2 - 2aS; where S = 150 meters coasting distance, v = 0 mps final velocity, and u = the answer from a). Solve for a, the acceleration.

c) k = sliding friction if and only if the boy locked his brakes. Proper braking would result in static (rolling) friction for the shortest distance stop. Friction force F = kmg = ma = f the net force on the bike/boy mass m. Therefore k = a/g and you solved for a in b) and g = 9.81 m/sec^2 on Earth's surface.

You can do the math. The physics is this. When friction is the only net force acting on a decelerating body (e.g., bike/boy, block of wood, car), the mass of the body is immaterial. m cancels out, leaving the accelerating (deceleration) a = kg; where k is the coefficient of friction sliding or rolling, makes no difference. Also, notice what happens on a slippery road, when k goes down. The car's deceleration goes down with the k, which is why we leave more room between us and the car in front when the road is wet and slippery.

2007-11-10 07:00:31 · answer #1 · answered by oldprof 7 · 0 0

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