Forces
A person is running on a track. Which of the following forces propels the runner forward?
The force of friction exerted by the ground on the person
How is the direction (+/-) of the velocity related to the position vs. time line?
A positive velocity is shown as a positive slope on the position vs. time graph. A negative velocity is shown as a negative slope on the position vs. time graph.
A student throws a rock horizontally from the edge of a cliff that is 20 m high. The rock has an initial speed of 10 m/s. If air resistance is negligible, the distance from the base of the cliff to where the rock hits the level ground below the cliff is most nearly
20 m
A planet with half Earth’s mass and half Earth’s radius is discovered. What would an astronaut who weighs 800 N on Earth weigh on the planet?
1600 N
Two objects, A and B, move toward one another. Object A has twice the mass and twice the speed of object B. Which of the following describes the forces the objects exert on each other when they collide and provides the best explanation?
The forces exerted by each object on the other are the same, because interacting objects cannot exert forces of different magnitude on each other.
How is the magnitude (absolute value) of the velocity related to the position vs. time line?
The magnitude of the velocity vs. time graph is shown as the slope value on the position vs. time graph. A greater magnitude means a steeper (higher) slope.
A ball is thrown with an initial speed of 20 m/s at an angle of 60° to the ground. If air resistance is negligible, what is the ball’s total speed at the instant it reaches its maximum height from the ground? Hint: what is the vertical velocity of the projectile at the top of it's motion?
10 m/s
Planet X has twice Earth’s mass and three times Earth’s radius. The magnitude of the gravitational field near Planet X’s surface is most nearly
2 N/kg
An elevator carrying a person of mass m is moving upward and speeding up. How does the magnitude F of the force exerted on the person by the elevator floor compare with the magnitude mg of the gravitational force?
F > mg
What is a Scalar?
are quantities that are fully described by a magnitude (or numerical value) alone.
An object is thrown with an initial speed near the surface of Earth. Assume that air resistance is negligible and the gravitational field is constant.
If the object is thrown horizontally, the direction and magnitude of its acceleration while it is in the air is
downward and constant
A hypothetical planet has a mass of twice that of the Earth and a radius of four times that of the Earth. What is the acceleration due to gravity on the planet in terms of g, the acceleration due to gravity at the Earth?
g/8
A truck collides head on with a less massive car moving in the opposite direction to the truck. During the collision, the average force exerted by the truck on the car is FT and the average force exerted by the car on the truck is FC. Which one of the following statements is correct?
FT will always be equal in magnitude to FC.
What is a vector?
are quantities that are fully described by both a magnitude and a direction.
A ball is thrown at an angle of 45 degrees above the horizontal. Which of the following best describes the acceleration of the ball from the instant after it leaves the thrower's hand until the time it hits the ground?
Always in the downward direction with the same constant value
A ball of mass m is attached to a vertical rod by two massless strings. The rod is rotated about its axis so that both strings are taut, with tensions T1 and T2, respectively. The strings and rod form the right triangle shown in the figure above. The ball rotates in a horizontal circle of radius r with speed v.
What is the tension T1 in the upper string?
mg/cos θ
Explain the differences between kinetic and static friction without using equations.
Kinetic friction is a force that opposes motion. Static friction is a force that acts on an object to resist the initiation of motion by an applied force. For a given interaction between two types of materials, static friction will increase with the applied force until it reaches a maximum value and the objects begin to move relative to each other. Kinetic friction is a constant and is less than the maximum value of static friction.
What is displacement?
is a vector quantity that refers to "how far out of place an object is"; it is the object's overall change in position.
A kitten sits in a lightweight basket near the edge of a table. A person accidentally knocks the basket off the table. As the kitten and basket fall, the kitten rolls, turns, kicks, and catches the basket in its claws. The basket lands on the floor with the kitten safely inside. If air resistance is negligible, what is the acceleration of the kitten-basket system while the kitten and basket are in midair?
The acceleration is directed downward with magnitude equal to g because the system is a projectile.
A 100 kg cart goes around the inside of a vertical loop of a roller coaster. The radius of the loop is 3 m and the cart moves at a speed of 6 m/s at the top. The force exerted by the track on the cart at the top of the loop is
200 N