Physics 105-001,3,4
Answers at the end
Review 2 for exam 1
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) gravity, normal, friction, and inertia
(b) gravity, normal, friction and the force of the kick
(c) gravity, normal and friction only
(d) gravity, normal, friction, inertia and the force of the kick
(e) 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 (c) 44 m (d) 176 m (e) impossible to determine without further information
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?
4 kg
40
M o
(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) straight south
(b) 12 degrees east of south
(c) 15 degrees east of south
(d) 12 degrees west of south
(e) 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) zero
(b) in the direction of the moon’s velocity
(c) directly away from the earth
(d) in the direction opposing the moon’s motion
(e) 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/s 2 ; the police car accelerates at the rate of 6 m/s 2 . 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 40 o
, 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 m
1
= 8 kg on a horizontal table, connected by a string to a mass m
2
= 5 kg hanging from a pulley. The coefficient of kinetic friction between the mass m
1
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

3a
4e
5d
6d
7b
8e
Answers
1c
2c
9. 8.0 s
10. 7.9 m
11. 1.36 m/s 2
12. 15.3 m/s
13. b
14. a
15. v x
= 4.0 m/s, v y
= -2.0 m/s; v = 4.5 m/s,

= 26.6
o
below x-axis.