Section 22 - Interactive problem: forces on a sliding block
22.1 Using the simulation in the interactive problem in this section, what are the direction and magnitude of (a) the weight, (b) the
normal force, (c) the frictional force, and (d) the tension that meet the stated requirements and give the desired acceleration?
(a) N, i. Straight up
ii. Straight down
iii. Up the plane
iv. To the right
(b) N, i. Straight up
ii. Straight down
iii. Up and to the left
iv. To the right
(c) N, i. Down the plane
ii. Up the plane
iii. To the right
iv. To the left
(d) N, i. Down the plane
ii. Up the plane
iii. Perpendicular to the plane
iv. Straight down
Section 23 - Hooke’s law and spring force
23.1 A 10.0 kg mass is placed on a frictionless, horizontal surface. The mass is connected to the end of a horizontal compressed
spring which has a spring constant 339 N/m. When the spring is released, the mass has an initial, positive acceleration of
10.2 m/s^2. What was the displacement of the spring, as measured from equilibrium, before the block was released? Watch the
sign of your answer.m23.2 Consider a large spring, hanging vertically, with spring constant k = 3220 N/m. If the spring is stretched 25.0 cm from
equilibrium and a block is attached to the end, the block stays still, neither accelerating upward nor downward. What is the
mass of the block?
kg23.3 A spring with spring constant k = 15.0 N/m hangs vertically from the ceiling. A 1.20 kg mass is attached to the bottom end of
the spring, and allowed to hang freely until it becomes stationary. Then, the mass is pulled downward 10.0 cm from its resting
position and released. At the moment of its release, what is (a) the magnitude of the mass's acceleration and (b) the
direction? Ignore the mass of the spring.
(a) m/s^2
(b) i. Downward
ii. Upward
23.4 A 5.00 kg wood cube rests on a frictionless horizontal table. It has two springs attached to it on opposite faces. The spring on
the left has a spring constant of 55.0 N/m, and the spring on the right has a spring constant of 111 N/m. Both springs are
initially in their equilibrium positions (neither compressed nor stretched). The block is moved toward the left 10.0 cm,
compressing the left spring and stretching the right spring. (a) Calculate the resulting net force on the block. (b) Calculate the
the initial acceleration of the block when it is released. Use the convention that to the right is positive and to the left is
negative.
(a) N
(b) m/s^2
23.5 A man steps on his bathroom scale and obtains a reading of 243 lb. The spring in the scale is compressed by a displacement
of í0.0590 inches. Calculate the value of its spring constant in (a) pounds per inch (b) newtons per meter.
(a) lbs/in
(b) N/mSection 24 - Air resistance
24.1 A parachutist and her parachuting equipment have a combined mass of 101 kg. Her terminal velocity is 5.30 m/s with the
parachute open. Her parachute has a cross-sectional area of 35.8 m^2. The density of air at that altitude is 1.23 kg/m^3. What is
the drag cofficient of the parachutist with her parachute?