1) A 1000-kg car is moving at 30 m/s around a horizontal unbanked curve whose di
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Question
1) A 1000-kg car is moving at 30 m/s around a horizontal unbanked curve whose diameter is 0.20 km. What is the magnitude of the friction force required to keep the car from sliding? A) 9800 N B) 300 N D) 9000 N E) 3000 N 2) A hypothetical planet has a mass of one-half that of the earth and a radius of twice that of the earth. t is the acceleration due to gravity on the planet in terms of g, the acceleration due to gravity at the surface of the earth? A) g/16 B) g/8 C) g/4 D) 8/2 E)g 3) The reason an astronaut in an earth satellite feels weightless is that A) the astronaut's acceleration is zero. B) the astronaut is at a point in space where the effects of the moon's gravity and the earth's gravity cancel. C) this is a psychological effect associated with rapid motion. D) the astronaut is beyond the range of the earth's gravity. E) the astronaut is falling. 4) If Earth had twice its present mass but it orbited at the same distance from the sun as it does now, its orbital period would be A) 6 months. B) 1 year. C)2 years D) 3 years. E)4 years. 5) Two equal-magnitude forces are applied to a door at the doorknob. The first force is applied perpendicular to the door, and the second force is applied at 30° to the plane of the door. Which force exerts the greater torque about the door hinge? A) the first force (applied perpendicular to the door) B) the second force (applied at an angle) C) Both forces exert zero torque. D) Both forces exert equal non-zero torques. 6) A 60.0-kg man stands at one end of a 20.0-kg uniform 10.0-m long board. How far from the man is the center of mass (or center of gravity) of the man-board system? A) 1.25 m B) 2.50 m C)5.00m D)7.50m E) 9.00 m 7) At a certain instant, a compact disc is rotating at 210 rpm. What is its angular speed in rad/s? A) 11 rad/s B) 22 rad/s C) 45 rad/s D) 69 rad/s E) 660 rad/s 8) When a car is weighed, it is driven slowly on a horizontal floor over a scale that records a reading as the front wheels go over the scale, and then records a second reading as the rear wheels go over the scale. The weight of the car is equal to A) the weight under the front wheels. B) the weight under the rear wheels. C) the average of the two weights. D) the sum of the two weights. E) the difference of the two weightsExplanation / Answer
1. f = m a_c = m v^2 /r
f = 1000 x 30^2 / (0.10 x 10^3) = 9000 N
Ans:(D)
2. g = G M / R^2
a = G (M/2) / (2R)^2 = (G M / R^2) / 8 = g / 8
Ans(B)
3. (E) when a = g so astronaut is falling.
4. period is independent of mass of revolving object.
Ans(B) 1 year
5. torque = r x F = r F sin(theta)
sin(90) > sin(30)
Ans:(A)
6. x_cm = ( (0 x 60) + (5 x 20))/(60 + 20)
= 100 / 80
= 1.25 m
Ans(A)
7. w = 210 x 2 pi rad / 60s = 22 rad/s
ANs(B)
8. (D)
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