Spring 2012
Exam 2
Physics
111-104
111-106
Name _____________________________
1. A daring downhill skier is sliding down a steep slope that makes an angle 
370 with the horizontal direction.
The mass of the fully equipped skier is m = 80 kg, the coefficient of kinetic friction for the waxed skis on the
snowy slope is = 0.15.
1. Sketch a FBD indicating all forces acting on the skier as he accelerates down the slope. (5 pts.)
2. Calculate the magnitude of Normal Force (5 pts.)
3. Calculate the friction force (5 pts.)
4. Calculate the magnitude of his acceleration (5 pts.)
2. In a carnival ride, passenger gondolas are attached by cables 10-m long to a circular horizontal structure of
radius 2-m on top of a tall pole (see fig). The pole is rotated rapidly, swinging the gondolas around in a circle. The
cables make a 550 angle with the vertical.
1. Calculate the linear speed of the gondolas. (5 pts.)
2. Calculate the angular velocity of the gondola. (5 pts.)
3. Calculate the tension in a cable if the mass of passenger and
gondola is 100 kg. (5 pts.)
4. Calculate kinetic and potential energies of the gondola with
passenger ( total mass 100-kg). (5 pts.)
3. A spring is hold vertically with a 10-kg mass attached to one end. Additional force of magnitude 2.5.103 N
downward is able to hold the spring a distance of 10-cm from its equilibrium position.
1. Calculate the spring constant k of the spring. (5 pts.)
2. Calculate the force of the spring on mass m. (5 pts.)
3. Calculate the elastic energy in the spring at the location of 10-cm. (5 pts.)
4. Calculate a force needed to hold the mass at a location 12-cm from its equilibrium position. (5 pts.)
4. A particle of mass m = 3-kg is at a height h0 = 4m above the ground at the top of a smooth, frictionless slide.
The horizontal plane has a coefficient of friction  = 0.1. as in fig.
The mass is released from rest, slides
down the incline, slows down on the
horizontal plane and in 20 cm
encounters a spring (with spring
constant k = 12000 N/m). After that the
mass is shot backward and climbs again
on the incline.
1. Calculate the speed of the mass at
the bottom of the slide. (5 pts.)
2. Calculate the maximum extent to
which the spring is compressed before
it hurls the mass back in the direction
whence it came. (5 pts.)
3. Calculate the work done by the
friction force on the horizontal plane
before the mass stops. (5 pts.)
4. Calculate the maximum height the mass climbs on the way back. (5 pts.)
5. A quarterback of mass 100 kg, running at speed 10 m/s runs directly into the arms of a 150 kg tackler moving in
the opposite direction at 5 m/s. The impact occurs in one dimension in midair and lasts for 0.2 s, after which the
players are locked together.
1. Calculate the linear momentum of each individual player. (5 pts.)
2. Calculate the velocity of the composite mass after the collision. (5 pts.)
3. Calculate the impulse imparted to the quarterback by the tackler. (5 pts.)
4. Calculate the magnitude of the average force exerted by the tackler on the quarterback. (5 pts.)