Definitions
Newton's 1st law
Problems
inclined planes
General infomration
100
What term is used to describe the vector sum of all the forces acting on an object?
Net force
100
What is Newton's First Law of Motion, and how does it define the concept of inertia?
Newton's First Law states that an object will remain at rest or in uniform motion unless acted upon by an external force. Inertia is the resistance of an object to changes in its state of motion.
100
An elevator carrying a 120 kg pig accelerates upwards with an acceleration of 5 m/s2. What is the normal force on the Pig?
Weight of pig = 1200N
Applying Newton's 2nd law to the pig: N-1200 = ma = 120 x 5 = 600
N= 600 + 1200 = 1800N
100
Which arrow correctly represents the normal force acting on the block in the diagram below?
C
100
In what direction does the force of air resistance act?
Air resistance acts in the direction opposite the direction of an object’s motion.
200
Construct a free-body diagram of a car being towed.
200
A book is resting on a table. According to Newton's First Law, explain why the book remains stationary. What conditions would cause the book to move?
The book stays stationary because the forces (gravity and the table's support force) are balanced. It moves if an unbalanced force, like a push, acts on it.
200
What is the order of magnitude of the normal force experienced by a man standing on the Earth?
The mass of a man is about 100kg, this is 1000N. if the man is standing stationary on the Earth then there will be a normal force acting upwards to balance his weight.
200
Which arrow shows the friction force acting on the ball rolling down the slope in the diagram?
A
200
What happens to air resistance when an object accelerates?
In most cases, air resistance increases with increasing speed.
300
What happens to an object in motion when it experiences a nonzero net external force?
The object experiences an acceleration
300
A 5 kg box is pushed with a force of 10 N, but it doesn’t move. What is the force of friction acting on the box?
The friction force equals the applied force, friction=10 N since the box doesn’t move.
300
A free fall parachutist of mass 75 kg jumps out of a plane. A few seconds after the jump, the air resistance experienced is 450 N. What is the acceleration of the parachutist?
Weight of parachutist = 750N
Applying Newton's 2nd law: 750 - 450 = ma
a = 300/75 = 4 m/s2
300
A 10kg box rests on a frictionless slope as shown. What is The force acting down the slope?
The normal force acts at right angles to the slope so there is no component down the slope.
The component of the weight down the slope is 10x10xsin30° = 50 N
300
How does the coefficient of static friction for two surfaces in contact compare to the coefficient of kinetic friction for the same two surfaces?
The coefficient of static friction is larger than the coefficient of kinetic friction for the same two surfaces in contact.
400
The amount of force equal to 1 kg·m/s
defines what SI unit?
Newton
400
A block of mass 2 kg is placed on a surface with a coefficient of friction μ=0.3 What is the maximum force that can be applied horizontally before the block starts moving? (Take g=9.8 m/s2
400
A child of mass 35 kg sits on the swing as shown. What is the tension in each rope?
2T=mg
T= (350)/2= 175 N
400
A 10 kg box is placed on a smooth, frictionless slope inclined at an angle 45 to the horizontal, as shown in the figure below. What is the magnitude of the normal force acting perpendicular to the surface of the slope (g=10 m/s2)?
The normal force acts at right angles to the slope =mgcos(30)= 10(10)cos45=71 N
400
Distinguish between mass and weight.
Mass is the amount of matter in an object and is an inherent property of an object. Weight is not an inherent property of an object and is the magnitude of the force due to gravity acting on the object.
500
Briefly describe how applying the brakes to stop a bicycle is an example of force.
Force causes an acceleration, or a change in an object’s velocity. Applying the brakes decelerates the bicycle (accelerates it in the negative direction) and causes a change in the bicycle’s velocity because the bicycle slows down
500
A car travels along a road at a constant velocity of 20 m/s. The force of friction that pushes the car forwards is 1000 N. What is the force of air resistance acting on the car ?
Velocity is constant so Newton's 1st law ⇒ Forces are balanced
1000 N
500
Two masses as shown are suspended from a massless pulley. Calculate the acceleration of the 10 kg mass when masses are left free.
3.3 m/s2
500
Ahmed, who has a mass of 50.0 kg, slides down the banister at his grandparents’ house. If the banister makes an angle of 45.0° with
the horizontal, what is the normal force between Fernando and the banister?
Fgcos(45)= 50(10)cos(45)= 354 N
500
When a car is moving, what happens to the velocity and acceleration of the car if the air resistance becomes equal to the force acting in the opposite direction?
The acceleration is then zero, and the car moves at a constant velocity.