Laws of Motion
What is Newton's Second Law of Motion?
Fnet=m*a
This force is always opposite the motion (or intended motion) of an object
What is friction
If you have a mass of 50 kg, what is your weight? g=9.8m/s2 down
490 N down
What is the net force on a crate with a weight of 120 N, a tension force to the right of 60 N, and static friction opposing motion?
0 N
Static friction means it isn't moving
Sketch a FBD for a book at rest on a desk
There should be an arrow labeled Fg downwards from the box and an equal-length arrow upwards labeled FN
What do net forces cause?
This force's strength depends on 2 objects' mass and the distance between them
What is gravity
A box with a weight of 7 N is on a table and has 5 N of force applied to it to the left, with a frictional force of 2 N between it and the table. What is the net force on the box?
3 N left
On Earth, what is the weight of a large-screen TV that has a mass of 57 kg? g=9.8m/s2 down
558.6 N down
Sketch a FBD for a skydiver falling at terminal velocity.
There should be an arrow labeled Fg downwards from the box and an equal-length arrow upwards labeled Fair
What is Newton's First Law of Motion?
An object at rest will stay at rest and an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
This force is perpendicular to a surface
What is Normal Force.
A ball with a mass of 0.4 kg is tossed upwards with a net force of 6.7 N. What is the acceleration of the ball?
16.75 m/s2 upwards
A student pushes on a 6-kg box with a force of 18 N forward. The force of sliding friction is 4 N backward. What is the acceleration of the box?
2.33 m/s2 forward
A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance.
There should be an arrow labeled Fg downwards from the box and an equal-length arrow upwards labeled FN. There should be an arrow to the right label Fapp and a shorter arrow to the left labeled Ff
Define inertia
A property of matter to resist any change in its state of motion or rest.
This force is caused by a rope or cable
What is tension?
A dancer lifts his partner above his head with an acceleration of 1.5 m/s2 . The dancer exerts a force of 180 N. What is the mass of the partner?
120 kg
Football player A is moving forward with a velocity of 11 m/s and collides with player B who is stationary. If player A has a mass of 65 kg and player B has a mass of 85 kg, what is the final momentum of the players if they stick together?
715 kgm/s
pi=pf
11*65+0*85=715
A football is moving upwards towards its peak after having been booted by the punter. Neglect air resistance. Diagram the forces acting upon the football as it rises upward towards its peak.
There should be an arrow downwards labeled Fg
Newton's 3rd law states this, "For ...
What is "For every action force there is an equal and opposite reaction force."
There are 4 different kinds of friction, name them and link them by their similarities
Static friction & rolling friction
Kinetic or sliding friction & air resistance
Calculate the force that is needed to propel a rocket into space if the rocket has a mass of 18,000 kg and it takes the rocket 12 min to reach 10.9 km/s, the escape velocity for Earth’s gravity.
272,500N
First convert to seconds (12 min = 720 s) and m/s (10.9 km/s = 10,900 m/s).
Then calculate acceleration [(vf-vi)/t=(10,900-0)/720=15.14m/s2].
Last, F=ma=18000*15.14=272500 N
Two students are sitting on gym scooters, not moving, and push off of each other. If student A has a mass of 55 kg and moves left with a velocity of 9 m/s, and student B has a mass of 40 kg, what is the velocity of student B?
12.375 m/s right
pi=pf=0 (at rest to start)
0=55*-9+40*vb
495=40vb
Draw an FBD for a car is coasting to the right and slowing down.
There should be an arrow labeled Fg downwards from the box and an equal-length arrow upwards labeled FN. There should also be an arrow to the left labeled Ff