True-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 95. The exam period was 90 minutes. The mean score was 70.1; the median was 73. Click here to see page1 page2 of the formula sheet that came with the exam.

Two identical disks slide on a horizontal frictionless surface. Disk 1 is initially traveling in the positive x-direction at a speed v_{1}. Disk 2 is initially traveling in the positive y-direction at a speed v_{2}. The disks collide and stick together as shown in the figure below. The final speed of the two disks is v_{f} = 4 m/s, and they are traveling at an angle θ = 20°.

What is the initial speed v_{1} of disk 1 before the collision?

(a) v_{1} = 7.5 m/s (b) v_{1} = 9.1 m/s (c) v_{1} = 11.3 m/s

(a) v_{2} = 0 m/s (b) v_{2} = 1.1 m/s (c) v_{2} = 2.7 m/s

(T) True (F) False

A block with an initial speed v_{0}, is at the start of the hilly path shown in the figure below. There is no friction between the block and the path, except on the 12-m long stretch between points B and points C, where the kinetic friction coefficient is μ = 0.43.

What is the minimum initial speed of the block so that it passes the 9 m hill at point A?

(a) v_{0} = 7.2 m/s (b) v_{0} = 10.0 m/s (c) v_{0} = 13.3 m/s (d) v_{0} = 16.1 m/s (e) v_{0} = 19.9 m/s

What is the speed of the block when it reaches point B?

(a) 10 m/s (b) 20 m/s (c) 40 m/s

(a) H = 4.4 m (b) H = 9.9 m (c) H = 12.2 m (d) H = 15.3 m (e) H = 23.3 m

(a) smaller than H/2. (b) equal to H/2. (c) larger than H/2.

Two identical putty balls are suspended from the ceiling by two massless strings as shown in the figure below. The two strings have the same length. Ball 1 is held at rest at point A, 0.4 m above ball 2, which is freely hanging. Ball 1 is then released, collides with ball 2 at point B and and sticks to it. Both balls then go up together and reach a maximum height h at point C.

When ball 1 travels from point A to point B, the work done by the tension in the string is

(a) positive. (b) zero. (c) negative.

(a) 0 m/s (b) 1.7 m/s (c) 2.8 m/s

(a) 0.1 m (b) 0.2 m (c) 0.4 m (d) 0.8 m (e) 1.6 m

(a) x = 2.0 m (b) x = 2.3 m (c) x = 2.5 m

A block of mass 0.25 kg moves at a speed of 1.5 m/s on a frictionless horizontal surface. The block then hits a wall and bounces back. After the collision with the wall, the block is traveling at the same speed and in the opposite direction compared to before the collision.

Calculate the change in the kinetic energy of the block?

(a) ΔKE = 0 J (b) ΔKE = 0.28 J (c) ΔKE = 0.56 J

(a) 0 kg m/s (b) 0.38 kg m/s (c) 0.53 kg m/s (d) 0.75 kg m/s (e) 0.97 kg m/s

(a) 0.002 sec (b) 0.003 sec (c) 0.004 sec

A uniform beam 4 meters long is attached to the ceiling by a string 1.5 meters from the left end of the beam. The left end of the beam is attached to the floor by another string. A 7 kg block is hanging from the right end as shown in the figure.

What is T_{F} the tension in the string attached to the floor if the beam is massless?

(a) T_{F} = 68.6 N (b) T_{F} = 114 N (c) T_{F} = 172 N

(a) T_{F} = 150 N (b) T_{F} = 176 N (c) T_{F} = 208 N

(a) increase. (b) remain unchanged. (c) decrease.

An 8 kg weight is attached to a 6 kg weight over a pulley as shown in the figure. The pulley is a uniform disk with moment of inertial I = 2 kg m^{2} and radius R = 0.4 meters as shown in the figure. The blocks start from rest, and after the 8-kg block has fallen a distance h, it is observed to be traveling at 3 m/s.

What is the mass of the pulley?

(a) 15 kg (b) 20 kg (c) 25 kg

(a) K_{p} = 11 J (b) K_{p} = 18 J (c) K_{p} = 23 J (d) K_{p} = 36 J (e) K_{p} = 56 J

(a) h = 0.46 m (b) h = 1.5 m (c) h = 3.2 m (d) h = 6.1 m (e) h = 8.2 m

(a) > 3 m/s (b) = 3 m/s (c) < 3 m/s

(a) W_{disk } > W_{hoop} (b) W_{disk } = W_{hoop} (c) W_{disk } < W_{hoop}

Two masses are attached to a two-meter massless beam that has been bent in the center and which is balancing on a fulcrum as shown in the figure. The left side of the beam is horizontal and has a 1 kg mass suspended from the end. The right side of the beam, makes an angle of 35° above the horizontal, and has an unknown mass suspended as shown in the figure. The system is in equilibrium

Calculate m the mass of the object attached to the right side of the beam.

(a) 1 kg cos(35°) (b) 1 kg sin(35°) (c) 1 kg (d) 1 kg / sin(35°) (e) 1 kg / cos(35°)

(a) rotate counter clockwise (the 1 kg mass will go down). (b) remain stationary. (c) rotate clockwise (the 1 kg mass will go higher up).