Physics Unit 3

A 50.0 N box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is 0.50, and the coefficient of kinetic friction is 0.30. A horizontal 20.0 N force is then exerted on the box. The magnitude of the acceleration of the box is most nearly

0 m/s2

The cart of mass 10 kg shown above moves without frictional loss on a level table. A 10 N force pulls on the cart horizontally to the right. At the same time, a 30 N force at an angle of 60° above the horizontal pulls on the cart to the left. What is the magnitude of the horizontal acceleration of the cart?

0.5 m/s2

The figure above shows the forces exerted on a block that is sliding on a rough horizontal surface: The weight of the block is 500 N, the normal force is 500 N, the frictional force is 100 N, and there is an unknown force F exerted to the right. The acceleration of the block is 0.4 m/s2. The value of F is most nearly

120 N

The figure above shows the forces exerted on a block that is sliding on a horizontal surface: the gravitational force of 40 N, the 40 N normal force exerted by the surface, and a frictional force exerted to the left. The coefficient of friction between the block and the surface is 0.20. The acceleration of the block is most nearly. . .

2.0 m/s2 to the left

A block of mass 2 kg slides along a horizontal tabletop. A horizontal applied force of 12 N and a vertical applied force of 15 N act on the block, as shown above. If the coefficient of kinetic friction between the block and the table is 0.2, the frictional force exerted on the block is most nearly

7 N

To overcome static friction, 10N of force was used to start a box moving. Which is true?

<10 N is needed to keep it moving at a constant speed.

Three identical blocks each take a different path from a height h to the ground. Block A is released from rest and falls vertically. Block B is released from rest and slides down a frictionless incline. Block C is projected horizontally with an initial speed v.

B

What direction does friction always act on an object?

In the opposite direction of the object's velocity.

If the net force acting on an object is 0, what must be true of the object?

It is not accelerating.

An object slides across a horizontal surface such that it slows down due to the force of friction that is exerted on the object. The object and the direction of its displacement are shown in the figure. Which of the following free-body diagrams could represent the forces that are exerted on the object?

Normal force and Force of Gravity are equal while friction is pointing to the left

A box is given a sudden push up a ramp. Friction between the box and the ramp is not negligible. Which of the following diagrams best represents the directions of the actual forces acting on the box as it moves upward after the push?

Normal force is parallel to the surface and the force of gravity is pointed straight down while friction is going towards the left

A student wants to investigate the motion of a ball by conducting two different experiments, as shown in Figure 1 and Figure 2 above. In Experiment 1, the student releases a ball from rest and uses a slow-motion camera to film the ball as it falls to the ground. Using video analysis, the student is able to plot the ball's horizontal position x and vertical position y as a function of time t. In Experiment 2, the student horizontally rolls the same ball off a table, and uses video analysis to plot the ball's horizontal position xand vertical position y as a function of time t starting from the instant the ball leaves the table. The graphs from each experiment are shown above along with each graph's best-fit curve line.

Since the balls have the same vertical position at any given time, they reach the ground at the same time.

Balls 1 and 2 are each thrown horizontally from the same height above level ground, but ball 2 has a greater initial velocity after leaving the thrower's hand. If air resistance is negligible, how do the accelerations of the balls and the times it takes them to hit the ground compare?

The acceleration and the time it takes to hit the ground are equal

A student predicts that a block sliding down a ramp inclined at 45 degrees should have an acceleration of approximately 7 m/s2. The block is released from rest, and the student measures the distance the block travels and the time it takes to travel that distance. The student determines that the block's acceleration is only 5.5 m/s2. Which of the following is the most likely reason for the difference between the predicted and calculated accelerations?

The student's model used to make the prediction did not account for all of the forces that are exerted on the block.

A student is tasked with using a force table to balance a small ring in the center of a pin, as shown in Figure 1. For each of the four strings shown, one end is attached to the small ring, and the other end is attached to a hanger that can hold masses. Each string is wrapped around a pulley so that the hanger and masses are at rest. The location of each pulley may be changed. Figure 2 shows a top-down view of the free-body diagram of the forces exerted on the pin at a particular moment in time. From a top-down perspective, in what direction will the pin accelerate?

Up and to the left

The process of breaking down vectors into their components is called:

Vector Resolution

The force exerted by 1 surface on another when there is no relative motion by the 2 surfaces

static friction