EF 157 - Fall 2006 – Exam 3 - Page 1 of 4
Name _____________________________________
g = 9.81 m/s2 = 32.2 ft/s2
Earth: Mass = 5.97 x 1024 kg, Radius = 6.38 x 106 m
1 hp = 550 ft-lb/s
G = 6.67 x 10-11 N•m2/kg2
Moon: Mass = 7.35 x 1022 kg, Radius = 1.74 x 106 m
1 ft-lb/s = 1.356 W
1) (15 pts) You are on a leaking ship and in order to keep it from sinking, it is necessary to pump 720 lb of
water up a height of 7.8 ft and over the side of the ship every minute. You have a "bilge pump" that
consumes 220 W of electricity and has an efficiency rating of 0.63. Will your ship sink or stay afloat? You
must justify your answer with calculations.
EF 157 - Fall 2006 – Exam 3 - Page 2 of 4
2) (25 pts) A 950 kg car [A] approaches an
intersection with a velocity of 16 m/s from
West to East. At the same time, a 1300 kg
minivan [B] approaches the same intersection
with a velocity of 21 m/s from South to North.
The two vehicles collide and stick together
(i.e., e = 0.0) as shown. Note, since the two
vehicles "stick together," you do NOT need to
identify or use the line-of-impact.
a) Find the speed (vf) and the direction of
travel (θ) of the wrecked vehicles
immediately after the collision.
b) Determine the percentage of energy lost in
the collision.
Name _____________________________________
N
W
E
S
A
B
EF 157 - Fall 2006 – Exam 3 - Page 3 of 4
Name _____________________________________
3) (25 pts) A 125 lb man acts as a human cannonball by
being "fired" from the spring-loaded cannon as shown. In
the launch position, the spring is compressed a distance of
2.75 ft and the distance the man is from the end of the
cannon is d = 8.25 ft. The angle θ = 37.5o and the inside
surface of the cannon is rough (μk = 0.275).
a) If the maximum acceleration the man can experience is
10.0*g = 322 ft/s2, determine the spring constant k of
the spring.
b) Using your answer to part a, determine the velocity of
the man as he leaves the cannon. Note, if you cannot
determine k (or you do not trust your answer), use k =
625 lb/ft.
EF 157 - Fall 2006 – Exam 3 - Page 4 of 4
Name _____________________________________
4) (35 pts) A 14000 kg truck and a 2100 kg
car have a head-on collision, Despite
attempts to stop, the truck has a velocity
of 6.6 m/s to the right and the car has a
velocity of 8.8 m/s to the left when they
collide. The coefficient of restitution is e = 0.65 and the collision occurs in 0.37 s.
a) Determine the velocities of the truck and the car after the collision.
b) Determine the percentage of energy lost in the collision.
c) Determine the average impulsive forces imparted to the truck and to the car during the collision.
d) Determine the average accelerations (decelerations?) of the truck and the car during the collision.
e) Which vehicle would you rather be in, and why? You must explain your answer.