Download Chapter 1 Quick Review

September 21-September 22, 2009
PHY 2048 Discussion Fall ’09
Conceptual Review: Chapter 5
A . Newton’s Law
1. Two forces are exerted on an object. Can the acceleration of the object be zero? If yes, under what
condition?
2. Two forces are exerted on a block of mass m. One of the forces F1 is along +x direction. The block
accelerates in the +y direction.
a)
Without any calculation, find which quadrant the 2 nd force is in?
b) Express F2 in unit-vector notation.
3. A block is on a horizontal surface. What are the reaction forces for the following forces: a) Normal
force exerted on the block. b) Gravitational force acting on the block
B. Some Particular Forces
1. A block is sliding down a frictionless slope of θ. Find the acceleration of the block and the normal force
exerted on the block.
2. Under what condition you can assume the tensions at both ends are the same?
3. Two blocks are connected by a string with a negligible mass. The surface is frictionless.
a) Choose a coordinate system for each block so that you can
express the acceleration of each block as common acceleration.
b) What are the acceleration and the tension?
4. A ball is dropped in an accelerating elevator. Express the acceleration of the ball relative to the elevator
in terms of tension.
September 21-22, 2009
PHY 2048 Discussion Fall ‘09
Practice Exam Problems (Chapter 5)
1. Equal forces F act on isolated bodies A and B. The mass of B is three times that of A. The magnitude of
the acceleration of A is: (Newton’s 2nd Law)
d. nine times that of B
a. three times that of B
b. 1/3 that of B
c. the same as B
e. 1/9 that of B
2. Mass differs from weight in that: (Mass & Weight)
weight is a force and mass is not
a. all objects have weight but some lack mass
c. the mass of an object is always more than its weight
b.
d. mass can
be expressed only in the metric system e. there is no difference
3. Two blocks (A and B) are in contact on a horizontal frictionless
surface. A 36-N constant force is applied to A as shown. The
magnitude of the force of A on B is: (Contact Force)
6.0 N
c. 29 N
d. 30 N
a. 1.5 N b.
e. 36 N
4. A feather and a lead ball are dropped from rest in vacuum on the Noon. The acceleration of the feather
is: (Gravitational Acceleration) a. more than that of the lead ball
less than that of the lead ball
d. 9.8 m/s
b. the same as that of the lead ball
c.
e. zero since it floats in a vacuum
5. A 1-N pendulum bob is held at an angle θ from the vertical by a 2-N
horizontal force F as shown. The tension in the string supporting the
pendulum bob (in newtons) is: (Tension)
a. cosθ
b. 2/cosθ
c. √5
d. 1
e. non of the above
6. A 90-kg man stands in an elevator that has a downward acceleration of 1.4 m/s2. The force exerted by
him on the floor is about: (Normal Force)
a. zero
b. 90 N c. 760 N d. 880 N e. 1010 N
7. A 70 N block and a 35-N block are connected by a string as shown. If
the pulley is massless and the surface is freictionless, the magnitude the
acceleration of the 35-N block is: (Block-String System)
3.3 m/s2
c. 4.9 m/s2
Answers: 1-a
2-b
3-d
d. 6.7 m/s2
4-b
5-c
6-c
e. 9.8 m/s2
7-b
a. 1.6 m/s2
b.