(Multiple choice)

(1)

Two objects of unequal mass are connected by a massless cord passing over a frictionless peg. After the objects are released from rest, which of the following statements are true? (U = gravitational potential energy, K = kinetic energy of the system.)

(a) ∆U < 0 and ∆K > 0 

(b) ∆U = 0 and ∆K > 0 

(c) ∆U < 0 and ∆K = 0 

(d) ∆U = 0 and ∆K = 0 

(e) ∆U > 0 and ∆K < 0

(2)

Two stones are thrown with the same initial speed at the same instant from the roof of a building. 

One stone is thrown at an angle of 30° above the horizontal; the other is thrown horizontally. (Neglect air resistance.) Which statement below is true? 

(a) The stones strike the ground at the same time and with equal speeds. 

(b) The stones strike the ground at the same time with different speeds. 

(c) The stones strike the ground at different times with equal speeds.  

(d) The stones strike the ground at different times with different speeds.

(3)

A woman on a bicycle traveling at 10 m/s on a horizontal road stops pedaling as she starts up a hill inclined at 3.0° to the horizontal. Ignoring friction forces, how far up the hill will she travel before stopping? 

(a) 5.1m 

(b) 30m 

(c) 97m 

(d) 10.2m 

(e) The answer depends on the mass of the woman.

(4)

A vertical spring compressed a distance x sits on a concrete floor. When a block of mass m1 is placed on the spring and the spring is released, the block is projected upward to a height h. If a block of mass m₂ = 2m₁ is placed on the spring and the spring is again compressed a distance x and released, to what height will the block rise?

(a) h/4

(b) h/2

(c) h/√2

(d) h

(5)

If the spring in Problem 10 is compressed an amount 2x when the block of mass m₂ is placed on it, to what height will the block rise when the spring is? Released?

(a) 2h

(b) √2 h 0

(c) h

(d) h/√2

(6)

A roller coaster car of mass 1500 kg starts a distance H = 23 m above the bottom of a loop 15 min diameter (Figure). If friction is negligible, the downward force of the rails on the car when it is upside down at the top of the loop is ­_________

(a) 4.6×104N

(b) 3.1×104N

(c) 1.7×104N

(d) 980 N

(e) 1.6 × 10³ N

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