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Practice Problems ---- sample test 2
1. Two ropes are attached to a 40-kg object. The first rope applies a force of 25 N and the
second, 40 N. If the two ropes are perpendicular to each other, what is the resultant
acceleration of the object?
a. 1.2 m/s2
b. 3.0 m/s2
c. 25 m/s2
d. 47 m/s2
2. Two blocks, joined by a string, have masses of 6.0 and 9.0 kg. They rest on a frictionless
horizontal surface. A 2nd string, attached only to the 9-kg block, has horizontal force = 30 N
applied to it. Both blocks accelerate. Find the tension in the string between the blocks.
a. 18 N
b. 28 N
c. 12 N
d. 15 N
3. A 250-kg crate is placed on an adjustable inclined plane. If the crate slides down the incline
with an acceleration of 0.70 m/s2 when the incline angle is 25, then what should the incline
angle be for the crate to slide down the plane at constant speed? (g = 9.8 m/s2)
a. 12
b. 21
c. 25
d. 29
4. A rock is rolled in the sand. It starts at 5.0 m/s, moves in a straight line for a distance of 3.0
m, and then stops. What is the magnitude of the average acceleration?
a. 1.8 m/s2
b. 4.2 m/s2
c. 5.4 m/s2
d. 6.2 m/s2
5. A spring is stretched 10.0 cm from equilibrium, and the potential energy stored is 80.0 J.
What is the value of elastic constant k of the spring?
a. 1.6 N/m
b. 16000 N/m
c. 10.6 N/m
d. 9.1 N/m
e. none of above
6.
A 9.0-kg hanging weight is connected by a string over a pulley to a 5.0-kg block sliding on a
flat table. If the coefficient of sliding friction is 0.20, find the acceleration of the system.
a. 1.9 m/s^2
b. 2.4 m/s^2
c. 3.2 m/s^2
d. 5.7 m/s^2
5 kg
T
T
9 kg
7.
Adisa gave a 40-N crate initial push down a 5.0-m long inclined plane at a constant velocity.
If the plane is inclined at an angle of 37 to the horizontal, what is the coefficient of kinetic
friction?
a. 0.75
b. 0.25
c. 2.25
d. 0.55
e. none of above
8
A 2 000-kg sailboat experiences an eastward force of 3 000 N by the ocean tide and a wind
force against its sails with magnitude of 6 000 N directed toward the northwest (45 N of W).
What is the direction of the resultant acceleration?
a. 60 N of E
b. 30 N of W
c. 30 N of E
d. 74 N of W
9. A 5kg rock is rolled in the sand. It starts at 5.0 m/s, moves in a straight line for a distance of
3.0 m, and then stops. What is the magnitude of the average force?
a. 4.9 N
b. 4.2 N
c. 5.4 N
d. 21 N
10. Rita accelerates a 0.40-kg ball from rest to 9.0 m/s during the 0.15 s in which her foot is in
contact with the ball. What average force does she apply to the ball during the kick?
a. 48 N
b. 72 N
c. 24 N
d. 60 N
11. A shot-putter moves his arm and the 7.0-kg shot through a distance of 1.0 m, giving the shot a
velocity of 10 m/s from rest. Find the average force exerted on the shot during this time.
a. 175 N
b. 350 N
c. 525 N
d. 700 N
12. In the terminology a 500-N block, the 500-N refers to the block’s:
a. mass.
b. force.
c. weight.
d. None of the above.
13. The statement by Newton that “for every action there is an opposite but equal reaction” is
regarded as which of his laws of motion?
a. first
b. second
c. third
d. fourth
14. Three forces, 5.0 N, 15.0 N, and 20.0 N, are acting on a 9.81-kg object. Which of the
following forces could also be acting on the object if it is moving with constant velocity?
a. 1.0 N
b. 19.0 N
c. 39.0 N
d. any of the above
15. A sled weighs 100 N. It is held in place on a frictionless 20 slope by a rope attached to a
stake at the top; the rope is parallel to the slope. What is the normal force of the slope acting
on the sled?
a. 94 N
b. 47 N
c. 37 N
d. 34 N
16. A 500-N tightrope walker stands at the center of the rope. If the rope can withstand a tension
of 1 800 N without breaking, what is the minimum angle the rope can make with the
horizontal?
a. 4
b. 8
c. 10
d. 15
17. A horizontal force of 750 N is needed to overcome the force of static friction between a level
floor and a 250-kg crate. If g = 9.8 m/s2, what is the coefficient of static friction?
a. 3.0
b. 0.15
c. 0.28
d. 0.31
18. A 100-kg box is placed on a ramp. As one end of the ramp is raised, the box begins to move
downward just as the angle of inclination reaches 15. What is the coefficient of static friction
between box and ramp?
a. 0.15
b. 0.27
c. 0.77
d. 0.95
19. A 2.00-kg ball has zero kinetic and potential energy. Ernie drops the ball into a 10.0-m-deep
well. Just before the ball hits the bottom, the sum of its kinetic and potential energy is:
a. zero.
b. 196 J.
c. 196 J.
d. 392 J.
20. A 20-N crate starting at rest slides down a rough 5.0-m long ramp, inclined at 25 with the
horizontal. 20 J of energy is lost to friction. What will be the speed of the crate at the bottom
of the incline?
a. 0.98 m/s
b. 1.9 m/s
c. 3.2 m/s
d. 4.5 m/s
21. A baseball outfielder throws a baseball of mass 0.15 kg at a speed of 40 m/s and initial angle
of 30. What is the kinetic energy of the baseball at the highest point of the trajectory? Ignore
air friction.
a. zero
b. 30 J
c. 90 J
d. 120 J
22. Which of the following is that form of energy associated with an object’s motion?
a. potential
b. thermal
c. bio-chemical
d. kinetic
23. Which of the following is that form of energy associated with an object’s location in a
conservative force field?
a. potential
b. thermal
c. bio-chemical
d. kinetic
24. What is the kinetic energy of a 0.135-kg baseball thrown at 40.0 m/s (90.0 mph)?
a. 54.0 J
b. 87.0 J
c. 108 J
d. 216 J
25. A horizontal force of 200 N is applied to a 55-kg cart across a 10-m level surface. If the cart
accelerates at 2.0 m/s2, then what is the work done by the force of friction as it acts to retard
the motion of the cart?
a. -1 100 J
b. -900 J
c. -800 J
d. -700 J
.
26. A 1 200-kg automobile moving at 25 m/s has the brakes applied with a deceleration of 8.0
m/s2. How far does the car travel before it stops?
a. 39 m
b. 47 m
c. 55 m
d. 63 m
27. A rock is thrown straight up with an initial velocity of 15.0 m/s. Ignore energy lost to air
friction. How high will the rock rise?
a. 1.53 m
b. 22.9 m
c. 6.50 m
d. 11.5 m
28. What is the minimum amount of energy required for an 80-kg climber carrying a 20-kg pack
to climb Mt. Everest, 8 850 m high?
a. 8.67 MJ
b. 4.16 MJ
c. 2.47 MJ
d. 1.00 MJ
29. A professional skier reaches a speed of 56 m/s on a 30 ski slope. Ignoring friction, what was
the minimum distance along the slope the skier would have had to travel, starting from rest?
a. 110 m
b. 160 m
c. 320 m
d. 640 m
e. none of above