Conceptual questions Flashcards
to understand the physics principles
an elevator suspended by a cable is descending at constant velocity. How many force vectors would be shown on a free-body diagram? Name them.
2 forces
tension and weight
the net force will be 0 on a free body diagram
since the elevator is descending with constant velocity , the forces must be balanced.
equal magnitude.
A compressed spring is pushing a block across a rough horizontal table. How many force vectors would be shown on a free-body diagram? Name them.
4 forces
normal force , weight, spring force and kinetic friction
A brick is falling from the roof of a three-story building. How many force vectors would be shown on a free-body diagram? Name them.
weight force
In Figure Q5.4, block B is falling and dragging block A across a table. How many force vectors would be shown on a free-body diagram of block A? Name them.
4 forces
weight, tension, kinetic friction and normal force
You toss a ball straight up in the air. Immediately after you let go of it, what force or forces are acting on the ball? For each force you name, (a) state whether it is a contact force or a long-range force and (b) identify the agent of the force.
gravitational force , its a long range force
maybe drag, its a contact force
Is the statement “An object always moves in the direction of the net force acting on it” true or false? Explain.
False.
This is because, if a object is already moving with constant velocity and the force is applied in the opposite direction. The object will first slow down, goes to 0 and then moves in the opposite direction
think of it as force = acceleration
Newton’s second law says F⃗ net=ma⃗ . So is ma⃗ a force? Explain.
no, ma is not a force.
if we go back to the definition of what is a force,
In otherwords, force is the CAUSE, and acceleration is the EFFECT. Newton’s second law says that the net force is the CAUSE of an object with mass to have an acceleration.
So mass multiplied by acceleration itself isn’t a force. It is a quantity that is caused to be that way, because of the net force acting upon the object.
Is it possible for the friction force on an object to be in the direction of motion? If so, give an example. If not, why not?
yes, it is possible.
check chegg for answers.
suppose you press your physics book against a wall hard enough to keep it from moving. Does the friction force on the book point (a) into the wall, (b) out of the wall, (c) up, (d) down, or (e) is there no friction force? Explain.
you have to draw this out.
once, you do, you realize that the answer is c
Static friction points opposite the direction in which the object would move if there were no friction. That is, it points in the direction necessary to prevent motion.
if there was no friction, it will fall down due to gravity
therefore, the arrow points up
Which, if either, of the basketballs in Figure Q5.16 are in equilibrium? Explain.
in equilibrium means that the net force is zero.
so, you will have to vector addition to check if fnet is zero or not
A car is parked on a steep hill. Identify the forces on the car.
there are three forces :
normal force, weight and static friction
A chandelier hangs from a chain in the middle of a dining room. Identify the forces on the chandelier.
2 forces :
Tension and weight
A baseball player is sliding into second base. Identify the forces on the baseball player.
3 forces :
kinetic friction, normal force and weight
A jet plane is speeding down the runway during takeoff. Air resistance is not negligible. Identify the forces on the jet
4 forces :
thrust, normal , weight and drag
An arrow has just been shot from a bow and is now traveling horizontally. Air resistance is not negligible. Identify the forces on the arrow.
2 forces :
drag and weight
there is no contact force