APPhys1: Live Review Problems

3/5 the tension in the string

A ball of mass m traveling at a constant speed v in a horizontal circle with a radius of 1.2 m. The ball is supported by a string of length 2.0 m. The net force acting on the ball is equal?

negative, negative, positive

A biker on a motorcycle is moving along a straight highway. The biker starts at a position x = -10 m. The biker is moving away from the origin and slowing down. What are the signs of the initial position, initial velocity, and acceleration?

negative, negative, negative

A biker on a motorcycle is moving along a straight highway. The biker starts at a position x = -10 m. The biker is moving away from the origin and speeding up. What are the signs of the initial position, initial velocity, and acceleration?

positive, negative, positive

A biker on a motorcycle is moving along a straight highway. The biker starts at a position x = 10 m. The biker is moving away from the origin and speeding up. What are the signs of the initial position, initial velocity, and acceleration?

longer than T/8

A block on a spring is oscillating, with an amplitude A, on a horizontal frictionless surface. To go through a full cycle, from +A to -A and back again, takes a time T. The block takes a time of T/4 (one quarter of the period) to move between +A and the equilibrium position (one quarter of the distance). How long does it take the block to move between +A and +A/2 (one eighth of the distance covered in a complete cycle)?

1 N

A box with a weight of 20 N is sitting at rest on the floor. Then, a 11 N force to the right is applied. The coefficient of static friction between the box and the floor is 0.50, while the coefficient of kinetic friction is 0.40. What is the magnitude of the net force acting on the box?

0 N

A box with a weight of 20 N is sitting at rest on the floor. Then, a 3 N force to the right is applied. The coefficient of static friction between the box and the floor is 0.50, while the coefficient of kinetic friction is 0.40. What is the magnitude of the net force acting on the box?

After the collision, both carts are moving together with a velocity v/3 to the right

A collision takes place between two carts on a horizontal track. Friction between the carts and the track can be neglected. Before the collision, cart A, with a mass of 2m, is traveling to the right with a speed v, while cart B, with a mass of m, is traveling to the left with a speed v. Which of these represents a possible outcome for the situation after the collision, that is consistent with the laws of physics?

a

A problem in a Physics book shows a runner moving to the left at 2.5 m/s approaching a stop sign 15 m away. The runner slows down at 0.3 m/s^2 and stops before she reaches the stop sign (which is considered to be at the origin). A student writes the data as follows: t0=0 s x0=+15 m v0=−2.5 m/s a=−0.3 m/s^2 Which of the variables is labeled incorrectly?

The battery current is doubled, but the current through the original bulb is unchanged, so the brightness of the original bulb does not change

A small incandescent light bulb is connected to a 6-volt battery. The bulb glows brightly. Assume the battery and the wires are ideal - assume they have no resistance. Another identical light bulb is placed in parallel with the original light bulb. What happens?

the resistance of the circuit increases, so the battery sends out less current and the original bulb gets dimmer

A small incandescent light bulb is connected to a 6-volt battery. The bulb glows brightly. Assume the battery and the wires are ideal - assume they have no resistance. Another identical light bulb is placed in series with the original light bulb. What happens?

C

An accident happens on the street, involving a small car driven by C traveling north and a large truck (about six times the mass of the car) driven by B that is traveling south. Which driver is likely to suffer the worst injuries in this collision? Assume other factors are equal, such as that the drivers are identical twins and are both wearing seat belts.

B>C>A

An object is traveling at 20 m/s east. It then experiences a collision, which changes the object's velocity. Here are three possible outcomes, stating the velocity of the object after the collision: A - the object is at rest B - the object is traveling at 10 m/s west C - the object is traveling at 10 m/s north Rank these situations based on the magnitude of the impulse experienced by the object during the collision. (Impulse is equal to the change in momentum.)

Yes

Can two objects experiencing identical net forces have different accelerations?

No

Does tension exert a force only in the direction of motion?

True

EVERY force occurs as one member of a pair of interaction forces.

4g

Earth and Planet V have the same mass density, but V has twice the radius of Earth. What is the strength of the gravitational fields on the surface of V compared to the surface of Earth (g)?

velocity and momentum

Joe tells you the following: "I throw a ball straight up in the air. After I release the ball, something about the ball decreases as the ball goes up, reaches zero for an instant at the highest point, and then increases again as the ball comes down." Air resistance can be neglected. Joe's statement correctly describes the magnitude of the ball's ...

False

Tension is the sum of the forces exerted at the ends of a string.

Momentum is conserved in this inelastic collision

Two steel balls collide and bounce apart in an isolated system. If the final kinetic energy is less than the initial kinetic energy, what of the following is true?

6 s

You are flying a plane horizontally, at a constant height of 180 meters, toward a tiny island, where a lone sailor has been shipwrecked. You will be dropping a package of food and water to this sailor, to keep them going until the rescue boat arrives. You calculate that, at the height you are at, the package will fall for five seconds before reaching the ground. Neglect air resistance. If you are currently 600 meters, measured horizontally, from the island, in how many seconds should you release the package so that it lands on the island? You release it with no initial velocity with respect to your plane.

7 s

You are flying a plane horizontally, at a constant speed of 50 m/s, toward a tiny island, where a lone sailor has been shipwrecked. You will be dropping a package of food and water to this sailor, to keep them going until the rescue boat arrives. You calculate that, at the height you are at, the package will fall for five seconds before reaching the ground. Neglect air resistance. If you are currently 600 meters, measured horizontally, from the island, in how many seconds should you release the package so that it lands on the island? You release it with no initial velocity with respect to your plane.

0.7v and 0.7T

You drop a ball from rest, and it falls through a height H to the ground in time T. Just before impact, its speed is v. Assume that the force of gravity is the only force acting on the ball while it falls. When the ball is dropped from a height of H, what will its speed be at height H/2 (halfway down) and how long will it take to reach height H/2?

v and T

You drop a ball from rest, and it falls through a height H to the ground in time T. Just before impact, its speed is v. You do this a second time, this time releasing the ball from a height of 2H. Assume that the force of gravity is the only force acting on the ball while it falls. When the ball is dropped from a height of 2H, what will its speed be at height H (halfway down) and how long will it take to reach height H?

1.4V and 1.4T

You drop a ball from rest, and it falls through a height H to the ground in time T. Just before impact, its speed is v. You do this a second time, this time releasing the ball from a height of 2H. Assume that the force of gravity is the only force acting on the ball while it falls. When the ball is dropped from a height of 2H, what will its speed be just before impact with the ground and how long will it take to reach the ground?

4D and 2T

You give a block an initial velocity on a horizontal surface. A constant force of friction acts on the block, slowing the block down and eventually bringing the block to rest. When you give the block an initial speed v, it slides for a distance D, and takes a time T to come to rest. How far, and for how much time, does the block slide when the initial speed is 2v?

Different V, Same Va

You have a turntable that can spin around an axis through its center with very little friction. You draw a line along a radius, from the center to the edge. On this line, you place one coin about halfway between the center and the edge, and a second, identical, coin closer to the edge. There is some friction between the coins and the turntable. You gradually increase the rotation rate of the turntable, and then let go - the turntable then spins at an approximately constant rate, with the coins remaining at rest with respect to the turntable. At a particular instant in time, how do their velocities (V) and angular velocities (Va) compare?

D/2

You stand on top of a building of height D, and release a ball from rest - it falls under the influence of gravity alone. At the instant you let that ball go, your friend Mariel fires a second ball straight up from the ground - that ball has the right speed to just reach the top of the building. After being launched, that ball is also influenced only by gravity alone. Where do the balls pass one another?

the tension

You tie a ball to a string, and you then set it oscillating, pendulum style. The support point stays fixed. As the ball passes directly below the support point (the string is vertical there), which is larger, the magnitude of the tension in the string, or the magnitude of the force of gravity acting on the ball?

4D and 2T

You toss a ball straight up into the air, giving it an initial speed V. After you release it, the ball is acted upon only by the force of gravity. The ball reaches a maximum height D (above the point you let it go) and takes a time T to reach that maximum height. You then fly to Mars and toss the ball straight up a second time, giving it an initial speed of V. If the gravity on Mars is half that on Earth, what is the maximum height now, and how long does it take to reach that maximum height?

D/2 and 2T

You toss a ball straight up into the air, giving it an initial speed V. After you release it, the ball is acted upon only by the force of gravity. The ball reaches a maximum height D (above the point you let it go) and takes a time T to reach that maximum height. You then fly to Mars and toss the ball straight up a second time, giving it an initial speed of V/2. If the gravity on Mars is half that on Earth, what is the maximum height now, and how long does it take to reach that maximum height?

16D and 4T

You toss a ball straight up into the air, giving it an initial speed V. After you release it, the ball is acted upon only by the force of gravity. The ball reaches a maximum height D (above the point you let it go) and takes a time T to reach that maximum height. You then toss the ball straight up a second time, this time giving it an initial speed of 4V. What is the maximum height now, and how long does it take to reach that maximum height?