PHYS-1401: College Physics-I
Ch-04
Name: _____________________________________
HOMEWORK PROBLEMS
Chapter 04: THE LAWS OF MOTION
NOTE:
Show your work, and circle the correct answer. Solve all questions and problems.
Any six problems will be graded and the marks for this HW will be based on these only.
Grading:
Max 3 points:
1 to 2 points:
0 point:
0 to 1 point:
-1 points:
for each (graded) answer worked and correct.
if worked out, but wrong.
if major blunder
if answer correct but no working.
for missing units in final answer (for those not MCQ)
Conceptual Problems
1.
A crate of weight W is being pushed across a horizontal surface by a force directed at an angle of
20° below the horizontal. What is the magnitude of the normal force on the crate?
a. It is less than W.
b. It equals W.
c. It is more than W.
2. An object weighs 100 N. If the gravitational constant G were half of what it is currently, what would
the weight of the object be?
a. 100 N
b. 50 N
c. 25 N
d. 200 N
3. A box of mass m is placed on an incline with angle of inclination θ. The box does not slide. The
magnitude of the frictional force in this case is:
a. μs mg sin θ.
b. mg cos θ.
c. mg sin θ.
d. not given.
4.1 Forces 4.2, 4.3, 4.3 Newton’s first, second and third laws
4.
Which of the following is an example of the type of force that acts at a distance?
a. gravitational
5.
b. magnetic
c. electrical
d. all of the above
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
1
PHYS-1401: College Physics-I
6.
Ch-04
A 7.0-kg bowling ball experiences a net force of 5.0 N. What will be its acceleration?
a. 35 m/s2
b. 7.0 m/s2
c. 5.0 m/s2
d. 0.71 m/s2
7.
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
8.
A 70.0-kg man jumps 1.00 m down onto a concrete walkway. His downward motion stops in 0.0200
seconds. If he forgets to bend his knees, what force is transmitted to his leg bones?
a. 15 500 N
b. 7 010 N
c. 4 900 N
d. 3 500 N
4.5 Applications of Newton’s Laws
9.
Find the tension in each cable supporting the 600-N cat burglar in Figure P4.17.
2
PHYS-1401: College Physics-I
Ch-04
10.
Two packing crates of masses 10.0 kg and 5.00 kg are connected by a light string that passes over
a frictionless pulley as in Figure P4.28. The 5.00-kg crate lies on a smooth incline of angle 40.0°. Find
the acceleration of the 5.00-kg crate and the tension in the string.
11.
Two objects with masses of 3.00 kg and 5.00 kg are connected by a light string that passes over a
frictionless pulley, as in Figure P4.38. Determine (a) the tension in the string, (b) the acceleration of
each object.
3
PHYS-1401: College Physics-I
Ch-04
4.6 Forces of Friction
12.
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
13. Doug hits a hockey puck, giving it an initial velocity of 6.0 m/s. If the coefficient of kinetic friction
between ice and puck is 0.050, how far will the puck slide before stopping?
a. 19 m
b. 25 m
c. 37 m
d. 57 m
14.
Three objects are connected on a table as shown in Figure P4.57. The rough table has a
coefficient of kinetic friction of 0.350. The objects have masses of 4.00 kg, 1.00 kg, and 2.00 kg as
shown, and the pulleys are frictionless. (a) Draw a free-body diagram for each object. (b)
Determine the acceleration of each object and each object’s directions. (c) Determine the
tensions in the two cords. (d) If the tabletop were smooth, would the tensions increase, decrease,
or remain the same?
4