Physics 150 Exam II Fall 1999
NAME:______
MC
Useful Constants and Data P
g0 = 9.81 m/s2G =6.670x10-11 N m2/kg2 / rearth = 6.38x106 m
mearth = 5.68x1024 kg
Part I Multiple Choice (4 points. ea.)
Choose the best answer
___ 1. The net work done on an object
(A) is equal to the change in the total energy of the object.
(B) is independent of the path of the object if there are no nonconservative forces acting on the object.
(C) has unites of Joules.
(D) all of the above.
___ 2. A roller coaster gain Potential Energy as it is pulled up to the start of the ride because gravity is
(A) a dissipative force
(B) a nonconservative force.
(C) a conservative force.
(D) a liberal force.
(E) any of the above depending upon the reference height
___ 3. When a second mass has the same speed but twice the mass of the first, then the second mass’s kinetic energy is
(A) twice that of the first.
(B) quadruple that of the first.
(C) the same as that of the first.
(D) one fourth that of the first.
(E) none of the above.
___ 4. A large mass collides elastically head on with a small mass which is initially at rest. After the collision, the large mass
(A) rebounds at a higher speed than the small mass, because energy an momentum are conserved.
(B) sticks to the small mass, slowing considerably because energy an momentum are conserved.
(C) continues in its original direction, but a lower speed.
(D) consumes the small mass, creating a wormhole to an alternate dimension.
(E) none of the above.
___ 5. When the momentum of given object is doubled,
(A) its velocity is halved.
(B) its potential energy is halved.
(C) its kinetic energy is quadrupled.
(D) its mass is doubled.
(E) none of the above.
___ 6. Kinetic energy is ____ , while momentum is _____
(A) a vector quantity , a scalar quantity.
(B) a scalar quantity, a vector quantity.
(C) a scalar quantity, also a scalar quantity.
(D) a vector quantity, also a vector quantity.
___ 7. In an elastic collision
(A) momentum is conserved but KE is not.
(B) KE is conserved but momentum is not.
(C) both KE and momentum are conserved.
(D) neither KE nor momentum are conserved.
(E) none of the above is always true.
___ 8. The acceleration of an object undergoing uniform circular motion is constant in
(A) direction only.
(B) magnitude only.
(C) neither magnitude and direction.
(D) both magnitude nor direction.
(E) none of the above is always true.
___ 9. The speed of an object in uniform circular motion is constant. The centripetal force needed if the radius of the circle is halved is
(A) half as great as before.
(B) twice as great as before.
(C) exactly the same as before.
(D) 4 times as great as before.
(E) none of the above.
___ 10. The gravitational acceleration of an object
(A) has the same value everywhere in space.
(B) has (approximately) the same value everywhere on the surface of the earth.
(C) is greater on the moon because of its smaller diameter.
(D) is zero on the moon because it is so far from the surface of the earth.
(E) none of the above.
2 Point Bonus: Does the orbital period of the planets get longer, shorter or remain the same, with increasing distance from the Sun?
Part II Problems
Show all work. No work = no credit! (15 points each)
1. A mass with an initial KE of 12.0 J is subjected to a force of magnitude 3.00 N applied in the direction same the mass’s initial motion.
(A) How much work is done on the mass by this force as the mass travels a distance of 2.00 m?
(B) What is the final KE of the mass?
Now another mass with an initial KE of 12.0 J is subjected to a force of magnitude 3.00 N applied in the direction opposite the mass’s initial motion.
(C) How much work is done on the mass by this force as the mass travels a distance of 2.00 m?
(D) What is the final KE of the mass?
2. A 30.0 kg boy running at 4.00 m/s runs and jumps on a stationary 8.00 kg sled on a frozen lake.
(A) What is the initial momentum of the sled?
(B) What is the initial KE of the sled?
(C) What is the initial momentum of the boy?
(D) What is the initial KE of the boy?
(E) What is the final momentum of the boy/sled (treated as a single object moving together) ?
(F) What is the final speed of the boy/sled?
(G) What is the final KE of the boy/sled?
(H) Was this an elastic or inelastic collision?
3. The coefficient of static friction between a car’s tires and the road is .300. The 2000 kg car is rounding a 200 m radius curve.
(A) What is the maximum force available due to static friction? (Note: this will be the maximum force available for the centripetal force necessary for the car not to slide off the road.)
(B) What is the maximum centripetal acceleration this car can take without slipping off of this curve?
(C) What is the maximum speed this car can go around the curve without slipping?
4. A 70.0 kg skier is at the top of a 5.00 m high icy (and hence frictionless) slope. At the top of the slope, the skier is moving a 8.00 m/s. Take all heights as measured from the bottom of the hill.
(A) What is the skier’s initial kinetic energy?
(B) What is the skier’s initial potential energy?
(C) What is the skier’s initial total energy?
(D) Is energy conserved in this problem?
(E) What is the skier’s final potential energy?
(F) What is the skier’s final kinetic energy?
(G) What is the skier’s final speed?”
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