1.During a workout, the football players at Rutgers State University ran up the

Question

1.During a workout, the football players at Rutgers State University ran up the stadium stairs at a steady pace in 56 s. The stairs are 80 m long and inclined at an angle of 43o. If a typical player has a mass of 118 kg, estimate the average power output on the way up. Ignore friction and air resistance.(g = 9.8 m/s2)

2A block rests on a horizontal, frictionless surface. A string is attached to the block, and is pulled with a force of 48.0 N at an angle above the horizontal. After the block is pulled through a distance of 15.5 m its speed is v = 2.70 m/s, and 55.0 J of work has been done on it.What is the mass of the block?

Explanation / Answer

net force is Fnet = m*a = m*g*sin(43)
a is the accelaration

distance travelled is s = 80m

time taken is t = 56 s

apply s = (u*t)+(0.5*a*t^2)

80 = 0.5*a*56^2

a = 0.051 m/s^2

then speed after t = 56 s is

v = u+(a*t) = 0 +(0.051*56) = 2.86 m/s

out put average power is P = F*v = m*g*sin(43)*2.85 = 118*9.81*sin(43)*2.85 = 2255.62 W

2) Work done W = F*S*cos(theta) = 55 = change in kinetic energy = 0.5*m*v^2 = 0.5*m*2.7*2.7 = 3.645

48*15.5*cos(theta) = 55 = 0.5*m*3.645

mass m of the block is m = 55/(0.5*3.645) = 30.18 kg

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