Physics 40 Chapter 5 Sample Lecture Problems
Starting from rest, Sally pulls Billy on the sled (total mass = 60kg)
with a total force of 100 N at an angle of 40 degrees above the
horizontal, as shown. After 5 seconds, how fast is the sled moving and
how far has it traveled from where it started?
Calculate your weight in N. 1 lb = 4.45 N Calculate your mass in kg.
The acceleration due to gravity on the surface of the moon is only 1/6 as it is on the Earth. What is
the weight of a 10-kg object on the moon and on the Earth? What is its mass on each?
Two 10 N weights are pulling on the spring scale as shown (the right side
is attached to a hook, the left side is attached to the body of the scale)
The reading on the scale is
a) 0 N
b) 10 N
c) 20 N
Problem
The magnitude of F1 is 75.0N and F2 is 50.0N. Ignore friction.
What is the acceleration of the block?
What if the friction between the block and the floor is 1.5N?
What is the acceleration of a sky diver when the air resistance equals ½ the total weight?
The Earth pulls on you, you pull on the Earth. You fall to the Earth, the Earth Falls to you.
You accelerate towards the Earth with g =9.8m/s2. With what acceleration is the Earth falling
towards you?
Statics Problem
Find the tensions in the wires.
T2
T1
43
55
W
Incline Plane Problem
Draw a free-body diagram of a
block which slides down a
frictionless plane having an
inclination of = 15.0°. If the
block starts from rest at the top
and the length of the incline is
2.00 m, find (a) the acceleration
of the block and (b) its speed
when it reaches the bottom of
the incline.
What do the Scales Read?
The three blocks are pushed across a rough surface by a 40-N force. If the
coefficient of kinetic friction between each of the blocks and the surface is 0.20,
determine the magnitude of the force exerted by m2 on m3.
m1 = 2kg , m2 = 3kg , m3 = 5kg
a)
b)
c)
d)
e)
20 N
30 N
10 N
15 N
25 N
A force F = 40 N pulls the two masses. If the table is frictionless, find the tension in the string.
m1 = 3kg , m2 = 1.5kg
a)
b)
c)
d)
e)
13 N
36 N
23 N
15 N
28 N
A constant force F pulls the system as shown. The pulleys are frictionless.
The coefficient of kinetic friction between the block and the table is μ .
a) Draw free body diagrams for both masses.
b) If the blocks are pulled a distance x, find the work done by friction in terms
of F , m1 , m2 , μ ,θ , g , x .
c) Find an expression for the acceleration in terms of F , m1 , m2 , μ , g ,θ .
In the figure shown, the coefficient of kinetic friction between the block and the incline is 0.29. Disregard any pulley
mass or friction in the pulley. Draw the free body diagrams for each mass. Derive a general solution for the acceleration
of the system in terms of M, θ, μ, and g, box it, then put the numbers in and get a numerical value – then box that too.
Then find a numerical value for the tension in the string. Box that. Show all your work and make it pretty! Use 3
significant figures.
2M
2M
30 30
30˚
M
M