D[ie]YNAMICS QUIZES

In the figure, what does the spring scale read? The pulleys are ideal and the strings and scale are also massless. (figure- scale w/ 1 N on each side)

exactly 1.0 N

In order to get a stationary object to start moving on a frictionless horizontal surface, you must exert a greater magnitude horizontal force on the object than the horizontal force that it exerts on you.

false

A projectile is launched with an initial velocity of 80 m/s at 30° above the horizontal. Neglecting air, what is horizontal component of the projectile's acceleration?

0 m/s2

A 50.0-kg crate is being pulled along a horizontal smooth surface. The pulling force is 10.0 N and is directed 20.0° above the horizontal. What is the magnitude of the acceleration of the crate?

0.188 m/s2

An object slides on a level floor. It slows and comes to a stop with a constant acceleration of magnitude 2.4 m/s2. What is the coefficient of kinetic friction between the object and the floor?

0.24

A cat leaps to try to catch a bird. If the cat's jump was at 60° off the ground and its initial velocity was 2.74 m/s, what is the highest point of its trajectory, neglecting effects of air?

0.29 m

A cart is initially at rest on a frictionless surface, and has exerted on it a net force of constant magnitude F. Measurements are taken of its acceleration a. Then the process is repeated with a force of different magnitude. The data are summarized in the graph above. What is the best estimate for the mass of the cart?

1.5 kg

A ball is thrown with an initial velocity of 20 m/s at an angle of 60° above the horizontal. If we can neglect air, what is the horizontal component of its instantaneous velocity at the exact top of its trajectory?

10 m/s

A net force accelerates a 4.5-kg tool at 40 m/s2. What acceleration would that same net force cause if it were exerted on an 18-kg tool?

10 m/s2

A block is on a frictionless table, on Earth. The block accelerates at 3.0 m/s2 when a 20 N horizontal force is exerted on it. The block and table are set up on the Moon where the freefall acceleration is 1.62 m/s2. The gravitational force exerted on the block by the Moon is closest to

11 N

The x component of vector is 8.7 units, and its y component is -6.5 units. The magnitude of is closest to

11 units

A boy jumps with a velocity of magnitude 20.0 m/s at an angle of 25.0° above the horizontal. What is the horizontal component of the boy's velocity?

18.1 m/s

If a vector has components Ax > 0, and Ay < 0, then the angle that this vector makes with the positive x-axis must be in the range

270° to 360°

You throw a rock horizontally off a cliff with a speed of 20 m/s. Assuming no effects of air, after 2.0 s, the magnitude of the velocity of the rock is closest to

28 m/s

A 6.0-kg box slides down an inclined plane that makes an angle of 39° with the horizontal. If the coefficient of kinetic friction is 0.40, at what rate does the box accelerate down the slope?

3.1 m/s2

The figure shows an acceleration-versus-force graph for a 125-g object. What should be the value of the first tick-mark on the vertical scale, as indicated by the arrow in the figure?

4

The x component of vector is 5.3 units, and its y component is -2.3 units. The angle that vector makes with the +x-axis is closest to

340°

A 450-kg sports car accelerates from rest to 100 km/h in 4.80 s. What is the magnitude of the net force exerted on a 68.0-kg passenger during the acceleration?

394 N

A person is using a rope to lower a 0.51-kg bucket into a well with a constant speed of 2.0 m/s. What is the magnitude of the force exerted by the rope on the bucket?

5.0 N

A hobbyist launches a projectile from ground level on a horizontal plain. It reaches a maximum height of 72.3 m and lands 111 m from the launch point. Assume no air. What was the angle of launch if g = 9.80 m/s2?

69.0°

What is the mass of an object that has a 685 N gravitational force exerted on it near Earth's surface, where g = 9.80 m/s2?

69.9 kg

A car of mass 1100 kg that is traveling at 27 m/s starts to slow down and comes to a complete stop in 578 m. What is the magnitude of the average stopping force exerted on the car?

690 N

When rolled down a mountainside at 7.0 m/s, the horizontal component of its velocity vector was 1.8 m/s. What was the angle of the mountain surface above the horizontal?

75°

The components of vectors and are given as follows: Bx = -9.2 Cx = -4.5By = -6.1 Cy = 4.3The angle (less than 180°) between vectors and is closest to

77°.

A ball thrown horizontally from a point 24 m above the ground, strikes the ground after traveling horizontally a distance of 18 m. With what speed was it thrown, assuming negligible air effects?

8.1 m/s

As shown in the figure, a 10-kg block on a perfectly smooth horizontal table is connected by a horizontal string to a 63-kg block that is hanging over the edge of the table. What is the magnitude of the acceleration of the 10-kg block when the other block is gently released?

8.5 m/s2

You push downward on a trunk at an angle 25° below the horizontal with a force of 750 N. If the trunk is on a flat surface and the coefficient of static friction between the surface and the trunk is 0.61, what is the most massive trunk you will be able to move?

81 kg

A boy kicks a football with an initial velocity of 20 m/s at an angle of 25° above the horizontal. If we neglect air, the magnitude of the acceleration of the ball while it is in flight is

9.8 m/s2.

If a vector has components Ax < 0, and Ay > 0, then the angle that this vector makes with the positive x-axis must be in the range

90° to 180°

A stone is thrown horizontally with an initial speed of 10 m/s from the edge of a cliff. A stopwatch measures the stone's trajectory time from the top of the cliff to the bottom to be 4.3 s. What is the height of the cliff if effects of air are negligible?

91 m

Two cars of equal mass have a head-on collision during a safety test. Car A has an initial velocity of 40 m/s, and car B has an initial velocity of -20 m/s. Which of the following choices describes the forces exerted by the cars on one another during the collision?

A exerts equal magnitude force on B as B exerts on A.

Mary and Debra stand on a snow-covered roof. They both throw snowballs with the same initial speed, but in different directions. Mary throws her snowball downward, at 30° below the horizontal; Debra throws her snowball upward, at 30° above the horizontal. Which of the following statements are true about just before the snowballs reach the ground below? Neglect the effects of air. (There could be more than one correct choice.)

Debra's snowball has exactly the same acceleration as Mary's snowball. Debra's snowball will stay in flight longer than Mary's snowball.

A block of mass m sits at rest on a rough inclined ramp that makes an angle θ with the horizontal. What must be true about the force of static friction f exerted on the block?

F = mg sin θ

If a vector pointing upward has a positive magnitude, a vector pointing downward has a negative magnitude.

False

A 5-kg cart is being pushed by a constant horizontal force on a frictionless surface. What would happen to the cart if the pushing force exerted on it were doubled in magnitude?

Its acceleration would double.

As shown in the figure, a woman is straining to lift a large crate, but without success. We denote the forces on the crate as follows: P is the magnitude of the upward force being exerted on the crate by the person, C is the magnitude of the vertical contact force on the crate by the floor, and W is the force that Earth exerts on the crate. How are the magnitudes of these forces related while the person is trying unsuccessfully to lift the crate?

P + C = W

As a person is sliding down a vertical rope, her grip steadily tightens. This action causes the upward frictional force that the rope exerts on her to increase also. What happens when the upward frictional force is exactly equal in magnitude the force exerted on her by Earth?

She will move at constant velocity

Two boxes are connected to each other by a string as shown in the figure. The 10-N box slides without friction on the horizontal table surface. The pulley is ideal and the string has negligible mass. What is true about the tension force T that the string exerts on the boxes?

T < 30 N

A hammer strikes a nail, driving it farther into a block of wood. Which of the following is the Newton's Third Law pair to the force that the hammer exerts on the nail?

The force that the nail exerts on the hammer.

Which of the following statements are true about an object in two-dimensional projectile motion if we neglect air?

The horizontal acceleration is always zero and the vertical acceleration is always a non-zero constant downward.

Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined ramp and allowed to slide down from rest without any air resistance. Which one of the following statements about these objects is correct?

The two objects reach the bottom of the ramp at exactly the same time.

Vector is along the +x-axis and vector is along the +y-axis. Which one of the following statements is correct with respect to these vectors?

The y component of vector is equal to the x component of vector

In an air-free chamber, a pebble is thrown horizontally, and at the same instant a second pebble is dropped from the same height. Compare the times of fall of the two pebbles.

They hit at the same time.

The magnitude of a vector can never be less than the magnitude of any of its components.

True

A person is pushing on a box exerting a force of magnitude P, as shown in the figure. Earth exerts a force W on the box. The push is directed at an angle θ below the horizontal, and the box remains a rest. The box rests on a horizontal surface that has some friction with the box. The force that the surface exerts on the box perpendicular to the surface is equal to

W + P sin θ.

A ball is launched from the ground at an angle, and follows the trajectory shown above. The ball experiences negligible air resistance, and passes through positions P, Q, and R, in order. Which of the following correctly represents the force(s) exerted on the ball at the three labeled positions?

all arrows pointing down only

A displacement vector is 34.0 m in length and is directed 60.0° east of north. Selecting from the choices in the table below, what are the components of this vector?

choice 4 north-17.0 m east-29.4 m

Which of the force diagrams above would correspond to an object that is being pushed to the right across a rough horizontal surface at a constant velocity?

equal fg and fn, equal horizontal forces

Which of the force diagrams above would correspond with an object that is sliding to the right across a horizontal frictionless surface at constant velocity?

figure- equal arrows up and down for normal and gravity no horizontal forces

Two objects of unequal masses, M and m (M > m), are connected by a very light cord passing over an ideal pulley of negligible mass. When released, the system accelerates, and friction is negligible. Which one of the following force diagrams most realistically represents the forces exerted on the two objects in the moving system?

figure- same upward force, more fg on larger

For general projectile motion if we neglect air, the horizontal component of a projectile's acceleration

is always zero.

Two boxes P and Q on a perfectly smooth horizontal surface are connected by a light horizontal cord. The mass of P is greater than that of Q. A horizontal force is exerted on box Q as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P is

less than F but not zero.

A player kicks a soccer ball in a high arc toward the opponent's goal. At the highest point in its trajectory

neither the ball's velocity nor its acceleration are zero.

wo blocks, A and B, are being pulled to the right along a horizontal surface by a horizontal 100-N pull, as shown in the figure. Both of them are moving together at a constant velocity of 2.0 m/s to the right, and both weigh the same. Which of the figures below shows a correct force diagram of the horizontal forces exerted on the upper block, A?

no horizontal forces act on A

The force diagram to the right corresponds to an object that is doing which of the following? (arrows only up and down)

remaining at rest moving at constant velocity

James and John dive from an overhang into the lake below. James simply drops straight down from the edge. John takes a running start and jumps with an initial horizontal velocity of 25 m/s. Assuming no effects of air, when they reach the lake below

the splashdown speed of John is larger than that of James.

A boulder rolls off of a very high cliff. If you disregard air, while it is falling, its trajectory is never truly vertical.

true