PHY 1A Misconceptual Problems
A railroad tank car contains milk and rolls at a constant speed along a level track. The milk begins to leak out the bottom. The car then
maintains a constant speed.
A golf ball is hit with a golf club. While the ball flies through the air, which forces act on the ball? Neglect air resistance.
The force of gravity acting on the ball.
Which pulls harder gravitationally, the Earth on the moon or the moon on the earth? Which accelerated more?
both the same, the moon accelerates more
You are riding in an enclosed train car moving at 90 km/hr. If you throw a baseball straight up, where will the baseball land?
in your hand
Assuming there is friction
tallest hill with steepest slope
While driving fast around a sharp right turn, you find yourself pressing against the car door. What is happening?
the door is exerting a rightward force on you
One ball is dropped vertically from a window. At the same instant, a second ball is thrown horizontally form the same window. Which ball has the greater speed at ground level?
the thrown ball (travels farther distance)
Two satellites orbit the earth in circular orbits of the same radius. One satellite is twice as massive as the other. Which statement is true about the speeds of these satellites?
the two satellites have the same speed
Two wheels having the same radius and mass rotate a the same angular velocity. One wheel is made with spokes so nearly all the mass is at the rim. The other is a solid disk. How do their rotational kinetic energies compare?
the wheels with spokes has about twice the KE
Which of the three kicks is in the air for the longest time? They all reach the maximum height h. Ignore air resistance
they are all the same
A bowling ball hangs from a cord i) a 200 g putty ball hits bowling ball ii) a 200 g rubber ball hits the bowling ball and bounces up. What happens
the bowling ball swings up farther in ii than in one. (*?*)
A small car and a heavy pickup truck are both out of gas. The truck has twice the mass of the car. After you push both the car and the truck for the same amount of time with the same force, what can you say about the momentum and the kinetic energy of the car and truck? Ignore friction.
they have the same momentum, but the car has more kinetic energy than the truck.
Consider a force F=80 N applied to a beam as shown. The length of the beam is l=5.0 m and theta is 37degrees, so that x=3 me and y=4m. Of the following expressions which ones give the correct torque produced by the force F around point P?
(80N*5m*sin37), (48N*5M), and (80N*3M)
What causes the boat to move forward?
The force the water exerts on the paddle.
Which of the following point towards the center of the circle in uniform circular motion?
acceleration, net force
A car travels 10 m/s east. Another car travels 10 m/s north. The relative speed of the first car with respect to the second is
less than 20m/s
A ball is thrown straight up. At what point does the ball have the most energy? Ignore air resistance.
everywhere, energy is always the same brah
In which of the following cases does a car have a negative velocity and a positive acceleration? A car that is traveling in the
-x direction decreasing in speed.
A car traveling at a velocity v can stop in a minimum distance d. What would be the car's minimum stopping distance if it were traveling at a velocity of 2v?
4d
You push a heavy crate down a ramp at a constant velocity. Only four forces act on the crate. Which force does the greatest magnitude of work on the crate?
force of friction
You drop a rock off a bridge. When the rock has fallen 4 m, you drop a second rock. As the two rocks continue to fall, what happens to their velocities?
Both increase at the same rate (actually asking about acceleration here bc looking at rate of velocity change, acceleration downward is constant).
An object at rest begins to rotate with a constant angular acceleration. If this object rotates through an angle theta in time t, through what angle did it rotate in time 1/2t?
1/4theta
You are in the middle of a large field. You walk in a straight line for 100m, then turn left and walk 100m more in a straight line before stopping. When you stop, you are 100m from your starting point. By how many degrees did you turn?
120 degrees (equilateral triangle)
At time t=0 an object is traveling to the right along the +x axis at a speed of 10 m/s with acceleration
2.0 m/s^2. Which statement is true?- The object will slow down, momentarily stopping, and then pick up speed moving to the left.
A 50N crate sits on a horizontal floor where the coefficient of static friction between the crate and the floor is 0.50. A 20N force is applied to the crate acting to the right. What is the resulting static friction force acting on the crate?
20N to the left (reverse of force applied)
A car accelerates from rest to 30 km/hr. Later, on a highway it accelerates from 30 km/h to 60 km/h. Which takes more energy, going from 0 to 30, or from 30 to 60?
30 to 60.
You are adding vectors of length 20 and 40 units. Which of the following choices is a possible resultant magnitude?
37 (have to find the max and min angles for distance)
When the speed of your car is doubled, by what factor does its kinetic energy increase?
4
Which of the following should be part of solving any problem in physics?
All of the above
A baseball is hit high and far. Which of the statements is true?
At the highest point, the magnitude of the velocity is the slowest.
When a skier skis down a hill, the normal force exerted by the skier by the hill is
less than the weight of the skier
A car travels along the x axis with increasing speed. We don't know the direction. Which of the following most clearly represents the motion of the car?
Concave down
A space shuttle in orbit around the earth carries its payload with its mechanical arm. Suddenly, the arm malfunctions and releases the payload. What will happen to the payload?
It will remain in the same orbit as the shuttle
A truck is traveling horizontally to the right. When the truck starts to slow down, the crate on the (frictionless) truck bed starts to slide. In what direction could the net force be on the crate?
No direction, the net force is zero.
The solid dot shown is a pivot point. The board can rotate about the pivot. Which force shown exerts the largest magnitude torque on the board?
Perpendicular and farthest away
You are trying to push your stalled car. Although you apply a horizontal force of 400 N to the car, it doesn't budge and neither do you. Which forces must also have a magnitude of 400 N?
The force exerted by the car on you, the friction force exerted by the car on the road, the friction force exerted by the road on you.
An astronaut is a short distance away from her space station without a tether rope. She has a large wrench. What should she do with the wrench to move toward the space station?
Throw it directly away from the space station.
A bullet fired from a rifle begins to fall
as soon as it leaves the barrel
A child whirls a ball in a vertical circle. Assuming the speed of the ball is constant (an approximation), when would the tension in the cord connected to the ball be greatest?
at the bottom of the circle
A ball is thrown downward at a speed of 20m/s. Choosing the +y axis pointing up and neglecting air resistance, which equations could be used to solve for other variables? The acceleration due to gravity is 9.8 m/s2 downward.
b) y=yo+(-20m/s)/t-(1/2)gt^2 and c) v^2=(20m/s)^2-2g(y-yo)
Two balls are thrown off a building with the same speed, one straight up and one at a 45 degree angle. Which statement is true if air resistance can be ignored?
both hit the ground at the same time and with same speed
A car drives at a steady speed around a perfectly circular track
both the acceleration and net force on the car point inward
Suppose an object is accelerated by a force of 100N. Suddenly a second force of 100 N in the opposite direction is exerted on the object, so that the forces cancel. The object
continues at the velocity it had before the second force was applied (*?*)
A small boat coasts at constant speed under a bridge. A heavy sack of sand is dropped from the bridge onto the boat. The speed of the boat
decreases
A car speedometer that is supposed to read the linear speed of the car uses a device that actually measures the angular speed of the tires. If larger
diameter tires are mounted on the car instead, how will that affect the speedometer reading? The speedometer-will read low.
A baseball player hits a ball that soars high into the air. After the ball has left the bat, and while it is traveling upward, what is the direction of acceleration?
downward
In a rotating vertical cylinder a rider finds herself pressed with her back to the rotating wall. Which is the correct free body diagram for her?
gravity downward, normal force away from wall and friction (up), nothing pushing against wall.
If there was a great migration of people toward the earth's equator, the length of the day would
increase because of conservation of angular momentum
A bear sling is used in some national parks for placing backpackers' food out of the reach of bears. As the backpacker raises the pack by pulling down on the rope, the force F needed:
increases, but the rope always sags where the pack hangs.
A person stands on a scale in an elevator. His apparent weight will be the greatest when the elevator
is accelerating upward.
A small mass m on a string is rotating without friction in a circle. The string is shortented by pulling it through the axis of rotation without any external torque, What happens to the tangential velocity of the object?
it increases
A small mass m on a string is rotating without friction in a small circle. The string is shortened by pulling it through the axis of rotation without any external torque. What happens to the angular velocity of the object?
it increases
The moon does not crash into earth because
it is freely falling but has a high tangential velocity
A man pushes a block up an incline at a constant speed. As the block moves up the incline,
it's potential energy increases and its kinetic energy stays the same.
You drive 4 km at 30 km/hr and then another 4 km at 50 km/hr. What is your average speed for the whole 8 km trip?
less than 40km/hr (40km/hr is average displacement)
To pull an old stump out of the ground, you and a friend tie two ropes to the stump. You pull on it with a force of 500 N to the north while your friend pulls with a force of 450 N to the northwest. The total force from the two ropes is
less than 950N (must break into components)
The magnitude of a component of a vector must be
less than or equal to the magnitude of the vector
Two identical billiar balls traveling at the same speed have a headon collision and rebound. If the balls had twice the mass, but mainteained the same size and speed, how would the rebound be different?
no difference
A bowling ball is dropped from a height h onto the center of a trampoline, which launches the ball back up into the air. How high will the ball rise?
no more than h, probs a little less
A satellite in circular orbit around the earth moves at constant speed. This orbit is maintained by the force of gravity between the earth and the satellite, yet no work is done on the satellite. How is this possible?
no work is done if the direction of motion is perpendicular to the force
You push very hard on a heavy desk, trying to move it. You do work on the desk
only if it starts moving
The space shuttle, in circular orbit around the earth, collides with a small asteroid which ends up in the shuttles storage bay. For this collision
only momentum is conserved
Choose the best answer in the previous question but assume you push both the same distance with the same force
same kinetic energy but the truck has more momentum than the car
If you used 1000J of energy to throw a ball, would it travel faster if you threw the ball ignoring air resistance
so that it wasn't rotating?
Suppose you are sitting on a rotating stool holding a 2kg mass in each outstretched hand. If you suddenly drop the masses, your angular velocity will
stay the same
A ping pong ball is shot into a circular tube that is lying flat (horizontal) on a tabletop. When the ping pong ball exits the tube, which path will it follow?
straight forward
A ball is dropped from the top of a tall building. At the same instant, a second ball is thrown upward from the ground level. When the two balls pass one another, one on the way up and the other on the way down, compare the magnitudes of their acceleration:
the acceleration of both balls is the same.
Which statements are not valid for a projectile? Take up as positive.
the acceleration of the projectile is positive and decreasing when the projectile is moving upwards, zero at the top, and increasingly negative as the projectile descends. And the velocity at the highest point is zero.
In the international space station which orbits earth, astronauts experience apparent weightlessness because
the astronauts and the station are in free fall towards the center of the earth
A baseball is pitched horizontally toward home plate with a velocity of 110 km/hr. In which of the following scenarios does the baseball have the largest change in momentum?
the baseball is hit straight back to the pitcher at a speed of 110 km/hr
A hunter is aiming horizontally at a monkey who is sitting in a tree. The monkey is so terrified when it sees the gun that if falls off the tree. At that very instant, the hunter pulls the trigger. What will happen?
the bullet will hit the monkey because both the monkey and the bullet are falling downward at the same rate due to gravity
You are pushing a heavy box across a rough floor. When you are initially pushing the box and it is accelerating,
the force you exert on the box is equal to the force of the box pushing back on you.
A golf ball and equal mass bean bag are dropped from the same height and hit the ground. The bean bag stays on the ground while the golf ball rebounds. Which experiences the greater impulse fro the ground?
the golf ball
Matt is able to move the large truck because
the ground exerts a greater friction force on Matt then it does on the truck.
Two spheres have the same radius and equal mass. One sphere is solid, and the other is hollow and made of a denser material. Which one has the bigger moment of inertia about an axis through its center?
the hollow one. Distribution of mass is important
A small solid sphere and a small thin hoop are rolling along a horizontal surface with the same translational speed when they encounter a 20degree rising slope. If these two objects roll up the slope without slipping, which will rise farther up the slope?
the hoop(*?* check)
A ball is thrown straight up. Neglecting air resistance, which statement is not true regarding the energy of the ball?
the potential energy decreases while the ball is going up.
Engines, including car engines, are rated in horsepower. What is horsepower?
the rate at which the engine can do work
Bonnie sits on the outer rim of a merry go round and Jill sits midway between the center and the rim. The rmerry go round makes one complete revolution every 2 seconds. Jills linear velocity is
the same as bonnies
The normal force on an extreme skier descending a very steep slope can be zero if
the slope is vertical
You are lying in bed and want to shut your bedroom door. You have a bouncy ball and a blob of clay both with the same mass. Which one would be more effective to throw at your door to close it?
the superball
A skier starts from rest at the top of each of the hills shown. On which hill will the skier have the greatest speed at the bottom if we ignore friction?
the taller hills, slope doesn't matter
A truck going 15 km/hr has a head on collision with a small car going 30 km/hr. Which statement best describes the situation?
they both have the same change in magnitude of momentum because momentum is conserves
A penny is placed on a turntable which is spinning clockwise as shown. If the power to the turntable is turned off, which arrow best represents the direction of the acceleration of the penny at point P while the turntable is still spinning but slowing down?
towards the center bc centripetal and rotation is slowing down
A ball is thrown straight up. What are the velocity and acceleration of the ball at the highest point in its path?
v=0, a=9.8m/s^2 down.