Download ROUND ALL NUMERICAL ANSWERS TO 3 SIGNIFICANT

ROUND ALL NUMERICAL ANSWERS TO 3 SIGNIFICANT FIGURES
Physics 251 sample exam 2
Dr. Ingram
PART A 10 questions 2 points each
In multiple choice questions circle all correct answers, if no answer is correct write in "none of the
above, the answer is ......."
1. A force acting on a particle is conservative if:
A.
B.
C.
D.
E.
its work equals the change in the kinetic energy of the particle.
it obeys Newton’s second law.
only when the work done by the resultant external force is zero.
its work depends on the end points of the motion, not the path between.
none of the above.
2. Which of the following is true:
A.
B.
C.
D.
E.
the center of mass of an object must lie within the object.
all the mass of an object is actually concentrated at its center of mass.
the center of mass of an object cannot move if there is zero net force on the object.
the center of mass of a uniform cylinder must lie on its axis.
none of the above.
3. The momentum of an object at a given instant is independent of its:
A. Inertia B. Mass C. Speed D. Velocity E. Acceleration
4. If two masses have the same kinetic energy, the ratio of their momenta are:
A. proportional to the ratio of their masses.
B. proportional to the ratio of the squares of their masses.
C. proportional to the ratio of the square roots of their masses.
D. inversely proportional to the ratio of their masses.
E. inversely proportional to the ratio of the square roots of their masses.
5. A ball is thrown into the air. As it rises, there is an increase in its:
A. acceleration
B. velocity
C. potential energy
D. kinetic energy
E. momentum
6. Which of the following is NOT dimensionally equivalent to energy?
A. Joule
B. N.m
C. kg.m2/s2
D. kilo-Watt.hour
E. kg.m2/s3
7. Which of the following is true for a perfect inelastic collision?
A. Kinetic energy is converted to potential energy and momentum is conserved.
B. Momentum is conserved, kinetic energy is not conserved and the colliding partners move off with
the same velocity.
C. Momentum is not conserved and the colliding partners move off together.
D. It is also an imperfect elastic collisions
8. A motor raises a 10 N load 5 m in 2 seconds. What is the average power of the motor?
A. 10 W
B. 20 W
C. 50 W
D. 200 W
E. None of the above, it is...
9. Find the recoil velocity of a gun that fires a 10 kg shell at 500 m/s if the gun weighs 700 kg
A. 100 m/s
B.714 m/s
C.358 m/s
D.97.5 m/s
E. None of the above, it is .....
10. A spring is compressed 25 cm from its relaxed state, if the spring constant of the spring is 500 N/m
how much energy is stored in the spring?
A. 37.5 J
B. 125 J
C. 31.2 J
D. 15.6 J
E. none of the above, it is .....
PART B 30 points in total
FOR FULL CREDIT ALL WORK MUST BE SHOWN & ALL PHYSICAL REASONING
GIVEN
10 points each
1. Box consists of 4 sides and a base but no top. The base and each side having the dimensions 20x20
cm2 and negligible thickness . A hole 8 cm in diameter has been cut in the center of one side. With
respect to the geometric center of the box, where is the center of mass of the box? The area of a circle is
pr2.
2. As a ball collides with a wall, the force on the ball goes linearly from zero to maximum in 3 ms (10-3
s), the force is then constant for 2 ms, the force then falls linearly to zero in 3 ms. The ball has mass of
50 g and an initial velocity of 30 m/s perpendicular to the wall. The ball rebounds with the same speed.
a. Draw a labeled graph of the force as a function of time
b. What is the impulse applied to the ball?
c. What is the maximum force applied to the ball?
d. What type of collision is this? Elastic or inelastic
3. A 40 kg block is dragged up a slope 5 m long and inclined at 30o to the horizontal at constant speed
with a force parallel to the surface of the plane. The coefficient of kinetic friction between the slope and
the block is 0.2.
a. What is the work done by the force?
b. At the top of the slope the block is stopped, then released. What is the kinetic energy of the block
when it reaches the bottom of the slope?