Problem 3: A car\'s bumper is designed to withstand a 4.0-km/h (1.I-m/s) collisi

Question

Problem 3: A car's bumper is designed to withstand a 4.0-km/h (1.I-m/s) collision with an immovable object without damaging the body of the car. The bumper cushions the shock by absorbing the force over a distance. Calculate the magnitude of the average force on a bumper that collapses o.185 m while bringing a 975-kg car to est from an initial speed of 1.4 m/s, in newtons. Numeric :A numeric value is expected and not an expression. Problem 4: A man in good physical condition can create 100 W of useful power for several hours at a stretch say by pedalin a mechanism that drives an electric generator. Neglecting any problems of generator efficiency and practical considerations such as resting time, answer the following questions about such a power generation method Part (a) How many people on such devices would it take to run a 4.2-kW electric clothes dryer? Numeric :A numeric value is expected and not an expression. Ndryer Part (b) How many people on such devices would it take to replace a large electric power plant that generates 820 Mw? Numeric: A numeric value is expected and not an expression. plant

Explanation / Answer

3)

Using work energy theorem

Work done by the net force = change in kinetic energy

F*S*cos(theta) = 1/2*m*(V^2 - Vo^2)

V is the final velocity = 0

Vo is the initial velocity = 1.4m/s

m = 975 Kg

S = 0.185 m

-F*0.185 = 975*(0^2 - 1.4^2)

F = 10330 N

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