Download 105ReviewExam1b

Physics 105-001,3,4
Review 2 for exam 1
Answers at the end
1. A man kicks a box, which then slides across the floor several meters before coming to a stop.
The floor is horizontal. While the box is moving, and no longer in contact with the man’s foot,
what forces are acting on the box? Ignore air resistance.
(a)
(b)
(c)
(d)
(e)
gravity, normal, friction, and inertia
gravity, normal, friction and the force of the kick
gravity, normal and friction only
gravity, normal, friction, inertia and the force of the kick
friction only
2. A ball is thrown horizontally from the top of a cliff of unknown height. The initial speed of
the ball is 20 m/s. If the ball reaches the ground 60 m horizontally from where it was thrown,
how high is the cliff?
(a) 20 m (b) 29 m
information
(c) 44 m (d) 176 m
(e) impossible to determine without further
3. Two blocks are connected by a string that passes over a massless, frictionless pulley. One
mass of 4.0 kg hangs down as shown, while the other is on a frictionless inclined plane. In order
to make the 4.0 kg mass move upward, the mass M must be greater than what minimum amount?
M
4 kg
40o
(a) 6.2 kg
(b) 5.2 kg
(c) 4.0 kg
(d) 2.6 kg
(e) 3.1 kg
4. A ball is thrown upward at an angle. Ignoring air resistance, during the motion of the ball does
its acceleration
(a) increase
(d) decrease
(b) increase and then decrease
(e) remain constant
(c) decrease and then increase
5. A stone with a mass of 10 grams drops from a truck traveling at a speed of 22 m/s and hits an
oncoming car which is traveling at a speed of 32 m/s. Which statement is true?
(a) The stone does not exert any force on the car
(b) The force exerted by the stone on the car exceeds the force exerted by the car on the stone
(c) The force exerted by the car on the stone exceeds the force exerted by the stone on the car
(d) The force exerted by the stone on the car has the same magnitude as the force exerted by the
car on the stone
(e) The stone exerts a force of 0.098 N on the car.
6. An airplane flies at an altitude of 11,000 m, in the jet stream where the air velocity is 150
km/hr to the east. The destination is 1000 km straight south. The air speed of the plane (the
speed with respect to the air) is 750 km/hr. The pilot must aim the plane
(a)
(b)
(c)
(d)
(e)
straight south
12 degrees east of south
15 degrees east of south
12 degrees west of south
15 degrees west of south
7. I throw a ball straight up at an initial speed of 25 m/s. How high does it rise? Ignore air
resistance.
(a) 13 m
(b) 32 m
(c) 25 m
(d) 63 m
(e) 9.8 m
8. Assume that the moon orbits the earth in a perfect circle, at a constant speed. The
acceleration of the moon is
(a)
(b)
(c)
(d)
(e)
zero
in the direction of the moon’s velocity
directly away from the earth
in the direction opposing the moon’s motion
toward the earth
Part II Problems. 10 points each
Show your work in the space provided, in order to be considered for partial credit. Please circle
your answer.
9. A motorist moving 40 m/s passes a stationary police car. The car immediately begins to
decelerate at the rate of -4 m/s2; the police car accelerates at the rate of 6 m/s2. How long does it
take for the police car to catch up to the motorist?
10. I kick a ball with a speed of 20 m/s, at an angle of 40o, toward a vertical wall that is 25 m
away. How high up the wall does the ball hit?
11. A half-Atwood’s machine consists of a mass m1 = 8 kg on a horizontal table, connected by a
string to a mass m2 = 5 kg hanging from a pulley. The coefficient of kinetic friction between the
mass m1 and the table is 0.40. What is the acceleration of this system?
12. A box is located in the middle of the flat bed of a pickup truck as the truck negotiates an
unbanked curve in the road. The curve is an arc of a circle of radius 40.0 m. If the coefficient of
static friction between box and truck is 0.60, how fast can the truck be moving without the box
sliding?
13. A driver slams on his brakes and skids for 25 m before colliding with another car. Given
that the coefficient of kinetic friction between the road and his tires is 0.60, what is the minimum
speed the car could have been going prior to the start of the skid?
(a) 25 m/s
(b) 17 m/s
(c) 150 m/s (d) 12 m/s
(e) Impossible to determine without knowing the mass of the car.
14.
A blue car of mass 1500 kg moving at 45 m/s rear-ends a red car of mass 1000 kg which
was moving 30 m/s before the collision. If the two cars lock together, what will be their speed
immediately after the collision?
(a) 39.0 m/s (b) 37.5 m/s (c) 45.0 m/s (d) 30.0 m/s (e) 39.7 m/s
15. An air hockey puck of mass 0.20 kg slides without friction at a speed of 6.0 m/s in the xdirection. It strikes a heavier, stationary puck of mass 0.30 kg which is initially at rest. If the
light puck moves at 3.0 m/s in the y-direction after the collision, what is the direction and
magnitude of the velocity of the heavier puck after the collision? Do not assume the collision is
elastic.
Before
after
Answers
1c
2c
3a
4e
5d
6d
7b
8e
9. 8.0 s
10. 7.9 m
11. 1.36 m/s2
12. 15.3 m/s
13. b
14. a
15. vx = 4.0 m/s, vy = -2.0 m/s; v = 4.5 m/s,  = 26.6o below x-axis.