Chapter 6: Applications of Newton’s Laws
1) A 10 kg wooden box is resting on a wooden floor. What is
the minimum horizontal force that must be applied to the box to
get it moving? The coefficient of static friction between the box
and the floor is 0.50. [49 N]
2) Once the box in the previous problem is moving, what force
must be applied to keep it moving at a constant speed if the
coefficient of kinetic friction between the box and the floor is
0.30? [29 N]
3) What force must be applied to the box in the previous
problem to accelerate it at 5.0 m/s2? (Assume it is already
moving, so consider kinetic friction.) [79 N]
4) A 10.0 kg box is placed at the top of a rough inclined
plane. It overcomes static friction and begins to slide. If the
coefficient of kinetic friction between the box and the plane is
0.300 and the angle of inclination of the plane is 40.0o, find the
acceleration of the box.
5) A 20.0 kg box is sliding across frictionless ice with a speed of
12.0 m/s when it hits a rough patch of ice where the coefficient
of kinetic friction is 0.250. How far along the rough ice does the
box slide before coming to rest? [29.4 m]
6) (see examples done in class and lab for connected objects
and for equilibrium)
7) problem 23 in text (two pulleys and a crate)
8) Two masses are connected by an ideal string passing over an
ideal pulley. One is on an incline and the other is hanging - see
diagram in class! Find the acceleration of the masses. (Mass on
incline is 7.00 kg and hanging mass is 12.0 kg. Angle of incline
is 37.0° and coefficient of friction between 7.00 kg mass and
incline is 0.250.)
9) Atwood’s machine – derive the expression for the
acceleration of the masses.
10) A 35.0 cm long spring hangs in a doorway. When a 7.50 kg
mass is attached to the bottom of the spring, it stretches so that
its total length is 41.5 cm. Find the spring constant of the
spring. (1130 N/m)
11) A rotating disk at a playground has a radius of 2.00 m. A
child sits on the outer edge. The coefficient of friction between
the disk and the kid’s pants is 0.224. Find the maximum speed
the outer edge of the disk can go before the child starts to slip
off. [2.10 m/s]