3. +-13 points Giancoli7 4.P.075 My Notes Ask Your Piles of snow on slippery roo

Question

3. +-13 points Giancoli7 4.P.075 My Notes Ask Your Piles of snow on slippery roofs can become dangerous projectiles as they melt. Consider a chunk of snow at the ridge of a roof with a pitch of 30° (a) What is the minimum value of the coefficient of static friction that will keep the snow from sliding down? (b) As the snow begins to melt, the coefficient of static friction decreases and the snow eventually slips. Assuming that the distance from the chunk to the edge of the roof is 5.6 m and the coefficient of kinetic friction is 0.20, calculate the speed of the snow chunk when it slides off the roof. m/s )If the edge of the roof is 9.5 m above ground, what is the speed of the snow when it hits the ground? m/'s 4. -3 points Giancoli7 4.P.OT9 My Notes Ask Your Te A 6480 kg helicopter accelerates upward at 0.61 m/s while lifting a 1220 kg frame at a construction site nig (a) What is the lift force exerted by the air on the helicopter rotors? (b) What is the tension in the cable (ignore its mass) that connects the frame to the helicopter? (c) What force does the cable exert on the helicopter?

Explanation / Answer

here,

3)

theta = 30 degree

a)

let the minimum coefficent of friction that will keep the snow from sliding be us

us = tan(theta)

us = tan(30) = 0.58

b)

uk = 0.2

the accelration , a = net force/effective mass

a= ( m * g * sin(theta) - uk * m * g * sin(theta)) /m

a = ( 9.81 * ( sin(30) - 0.2 * cos(30)))

a = 3.21 m/s^2

d = 5.6 m

the final speed , v = sqrt(2 * a * d)

v = sqrt(2 * 5.6 * 3.21) m/s

v = 6 m/s

c)

height , h = 9.5 m

let the final speed be v'

for vertical direction

v'y ^2 - (v * sin(theta))^2 = 2 * g * h

v'y^2 = ( 6 * sin(30))^2 + 2 * 9.81 * 9.5

vy' = 14 m/s

the final horizontal speed , v'x = v * cos(theta) = 5.2 m/s

the final speed , |v'| = sqrt(v'x^2 + v'y^2)

|v| = 14.9 m/s

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