Review problems for the "Newton's laws test"
10. A backpack is sitting on the floor of an elevator, which is accelerating upward. Which one of the
following statements about forces on the backpack is a true statement?
a. The normal force is egual to weight
b. The normal force is less than weight
c. The normal force is greater than weight
d. This question cannot be answered without knowing the exact acceleration rate of the elevator.
11. The free-body diagram below shows the forces acting on a racquetball while a woman is in the
midst of throwing it straight up high into the air. (The lengths of the arrows representing the forces
do not necessarily represent the relative strength of the forces.)
In the free-body diagram, the upward force is the force exerted by the woman, and the downward
force is the force exerted by the earth (the force of gravity). Assume there is no air resistance.
Which of the following statements is NOT true?
a. While the woman is throwing the racquetball, the magnitude of the average force she exerts on the
racquetball is greater than the magnitude of the force the earth exerts on the racquetball.
b. While the racquetball is in the air, the magnitude of the upward force on the racquetball is equal to
the magnitude of the force the earth exerts on the racquetball.
c. While the woman is throwing the racquetball, the magnitude of the force she exerts on the
racquetball is equal to the magnitude of the force the racquetball exerts on her.
d. While the racquetball is in the air, the magnitude of the force the earth exerts on the racquetball is
equal to the magnitude of the force the racquetball exerts on the earth.
e. While the woman is throwing the racquetball, the magnitude of the force the earth exerts on the
racquetball is equal to the magnitude of the force the racquetball exerts on the earth.
12.Two boxes of textbooks, of masses 10 kg and 15 kg, are connected by a lightweight string, and
then pulled across a horizontal table by a horizontal applied force, as shown in the diagram below.
The applied force has a magnitude of 50 N, and there is no friction between the boxes and table.
What is the acceleration of the 10 kg box?
f.
14 m/s2
b. 2 m/s2
c. 3.5 m/s2
d. 5 m/s2
13. In an experiment, a 100 kg student stands on a scale in an elevator that is accelerating upward at 4
m/s2. How many Newtons does the scale read?
10. 100 N
b. 400 N
c. 1000 N
d. 1400 N
14. In a junkyard, a crane with a giant magnet lifts cars. The magnet can apply a maximum force of
40,000 N. A certain truck weights 25,000 N. What is the maximum rate at which the magnet can
accelerated the truck upward while lifting it?
a. 4.28 m/s2 b. 0.600 m/s2
c. 1.67 m/s2
d. 5.88 m/s2
e. 7.35 m/s2
15.In the diagram below a 20 kg suitcase is dragged forward across a horizontal floor, by a 50 N force
exerted at 53 degrees above the horizontal. If the floor is frictionless, find the suitcase’s acceleration rate.
a. 0.5 m/s2 b. 1.5 m/s2
c. 2 m/s2
d. 2.5 m/s2
16. As shown in the diagram below, a 6 kg bowling ball is hung from a strong lightweight cord, over a
frictionless pulley at the edge of a flat table. The other end of the cord is attached to a 2 kg block on the
table, and there is no friction between the block and the table. What is the acceleration of the system
when released from rest?
a.5 m/s2
b. 7.5 m/s2
c. 10 m/s2
d. 30 m/s2
17. A toy car of mass M is released to slide down a ramp inclined at  degrees. The rotation of the
wheels and the friction on the incline are both negligible. What is the car’s acceleration down the
incline?
g. Mgsin b. Mgcos
c. gcos
d. gsin
13. A block of mass m is pulled across a horizontal floor by a force of magnitude F. The coefficient of
friction between the block and the floor is µ. Which of the following is a expression for the frictioanl
force exerted on the block?
h. µmg
b. µF
c. µmg – F
d. µmg + F
e. µ(mg – F)
14. . A block of mass m is accelerated across a rough surface by a force of magnitude f that is
exerted at an angle Φ with the horizontal, as shown below. The frictional force on the block exerted
by the surface has magnitude f.
What is the magnitude of the acceleration a of the block?
i.
b.
c.
12. Two blocks are tied to a lightweight string and hungover a frictionless pulley, as shown in the
diagram below. When released from rest, what is the acceleration of the 5 kg block?
a.
b.
c.
d.
5 m/s2
7.5 m/s2
10 m/s2
20 m/s2
14. Picture below is a 75 kg man hanging onto a rope that runs over a pole to a 55 kg box. If the friction
between the rope and pole is negligible, at what rate does the man have to accelerate (sliding) down the
rope so that the box is just on the verge of being lifted off the ground (but stays put)?
e. 0.26 m/s2 b. 0 m/s2
c. 0.73 m/s2
d. 2.61 m/s2
e. 2.04 m/s2