CU 2006 sp final exam key

# CU 2006 sp final exam key - PHYS2010 FINAL EXAM VERSION...

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PHYS2010 FINAL EXAM, VERSION 0001, SPRING 2006 1 Useful Constants Sea level atmospheric pressure: 101 kPa = 1 . 01 × 10 5 N/m 2 Density of water: 1.00 g/cm 3 = 1000 kg/m 3 Universal gravitational constant: G = 6 . 67 × 10 - 11 m 3 / (kg s 2 ) = 6 . 67 × 10 - 11 N m 2 / kg 2 Problems For the next two problems, you are ﬂoating in a spacesuit. At ﬁrst you have no velocity and no forces are acting on you. 1. You throw a ball of mass 1 kg so that it starts moving at 5 m/s. You and the spacesuit (without the ball) have a mass of 100 kg. What is your speed after you throw the ball? A) 0.05 m/s B) 0.5 m/s C) 0 m/s D) 5 m/s E) 15 m/s Momentum conservation says 0 = m 1 v 1 + m 2 v 2 , hence v 2 = - ( m 1 /m 2 ) v 1 , so . 05 m/s. 2. You caused the ball to move by applying a constant force for 0.5 s. What is the magnitude of the force exerted on you by the ball during that time? A) 0.5 N B) 1 N C) 5 N D) 10 N E) Not enough information given The force is the change in momentum over the change in time, so mv/t = 5 /. 5 = 10 N. By Newton’s third law the magnitudes of the forces (you on the ball or the ball on you) are the same. 3. Two motors are labeled 1 and 2. Both motors are designed to lift widgets from the ﬂoor of a warehouse to a high shelf. At its maximum power setting P 1 , motor 1 is capable of lifting a mass m 1 through a height diﬀerence h 1 in a time t 1 . Motor 2 can lift twice the mass of motor 1, but it takes twice as long: at maximum power P 2 , motor 2 can lift a mass 2 m 1 through a height h 1 in a time 2 t 1 . What is the relationship between the power outputs of the two motors? A) P 2 = 1 4 P 1 B) P 2 = 1 2 P 1 C) P 2 = 4 P 1 D) P 2 = 2 P 1 E) P 2 = P 1 Motor 1 can lift mass m 1 up h 1 : the work done in this case is W = m 1 gh 1 , so P 1 = W/ Δ t = m 1 gh 1 /t 1 . Similarly, P 2 = (2 m 1 ) gh 1 / (2 t 1 ) = m 1 gh 1 /t 1 , so P 2 = P 1 . 4. The vector A has magnitude | A | = 5 . 6, and makes an angle θ = 30 from the left with the positive y -axis (see diagram). To two-place precision, what is A x , the x -component of the vector A ? x y A =30 o A) +2 . 8 B) - 2 . 8 C) +4 . 8 D) - 4 . 8 E) None of these A x = - A sin θ = - (5 . 6)(0 . 5) = - 2 . 8 .

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PHYS2010 FINAL EXAM, VERSION 0001, SPRING 2006 2 5. A penny of mass m is resting on a box that is accelerating to the right, as shown below. The coeﬃcient of static friction between the penny and the box is μ S . When the acceleration of the box is slowly increased, the penny begins to slide just when the magnitude of the acceleration reaches a max = 15 m/s 2 . However, when the acceleration is maintained at a 0 = 10 m/s 2 , the penny stays in place on the box no matter what the velocity is. box a penny mass m " S Which of the following statements are true when the box’s acceleration is a = a 0 and the penny stays in place? I. The magnitude of the force of static friction is F fric = μ S mg . II. The magnitude of the acceleration of the penny is a 0 = 10 m/s 2 .
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CU 2006 sp final exam key - PHYS2010 FINAL EXAM VERSION...

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