PRE-ASSESSMENT - PHYS 206

In the figure, student a has a mass of 95 kg and student b has a mass of 77kg. They sit in identical office chairs facing each other. Student a places his bare feet on the knees of student b, as shown. Student a then suddenly pushes outward with his feet, causing both chairs to move. During the push and while the students are still touching one another:

each student exerts the same amount of force on the other.

The figure shows a boy swinging on a rope, starting at a point higher than A. Consider the following distinct forces: 1. A downward force of gravity 2. A force exerted by the rope pointing from A to O 3. A force in the direction of motion 4. A force pointing from O to A Which of the above forces is (are) acting on the boy when he is at position A?

1 and 2

Despite a very strong wind, a tennis player manages to hit a tennis ball with her racquet so that the ball passes over the net and lands in her opponent's court. Consider the following forces: 1. A downward force of gravity. 2. A force by the "hit". 3. A force exerted by the air. Which force(s) is (are) acting on the tennis ball after it has left contact with the racquet and before it touches the ground?

1 and 3

A ball is fired by a cannon from the top of a cliff as shown in the figure. Which of the paths would the cannon ball most closely follow?

B

Two metal balls are the same size but one weighs twice as much as the other. The balls are dropped from the roof of a single story building at the same instant of time. The time it takes the balls to reach the ground below will be:

about the same for both balls.

With the path you chose in the previous question, beyond the point c the speed of the rocket is:

constant

A rocket drifts sideways in outer space from point a to point b as shown in the figure. The rocket is subject to no outside forces. Starting at position b, the rocket's engine is turned on and produces a constant thrust (force on the rocket) at right angles to the line ab. The constant thrust is maintained until the rocket reaches a point c in space. With the path you chose in the previous question, as the rocket moves from position b to position c its speed is:

continuously increasing

A stone dropped from the roof of a single story building to the surface of the earth:

speeds up because of an almost constant force of gravity acting upon it.

If the woman in the previous question doubles the constant horizontal force that she exerts on the box to push it on the same horizontal floor, the box then moves:

with a continuously increasing speed.

An empty office chair is at rest on a floor. Consider the following forces: 1. A downward force of gravity. 2. An upward force exerted by the floor. 3. A net downward force exerted by the air. Which force(s) is (are) acting on the office chair?

1 and 2

Two metal balls are the same size but one weighs twice as much as the other. The two metal balls roll off a horizontal table with the same speed. In this situation:

both balls hit the floor at about the same horizontal distance from the base of the table.

A woman exerts a constant horizontal force on a large box. As a result, the box moves across a horizontal floor at a constant speed vo. The constant horizontal force applied by the woman:

has the same magnitude as the total force which resists the motion of the box.

The figure shows a frictionless channel in the shape of a segment of a circle with its center at O. The channel has been anchored to a frictionless horizontal table top. Forces exerted by the air are negligible. You are looking down at the table. A ball is shot a high speed into the channel at p and exits at r. Consider the following distinct forces: 1. A downward force of gravit 2. A force exerted by the channel pointing from q to O 3. A force in the direction of motion 4. A force pointing from O to q Which of the above forces is (are) acting on the ball when it is within the frictionless channel at position q?

1 and 2

A boy throws a steel ball straight up. Consider the motion of the ball only after it has left the boy's hand but before it touches the ground, and assume that forces exerted by the air are negligible. For these conditions, the force(s) acting on the ball is (are):

An almost constant downward force of gravity only.

A rocket drifts sideways in outer space from point a to point b as shown in the figure. The rocket is subject to no outside forces. Starting at position b, the rocket's engine is turned on and produces a constant thrust (force on the rocket) at right angles to the line ab. The constant thrust is maintained until the rocket reaches a point c in space. At point c the rocket's engine is turned off and the thrust immediately drops to zero. Which of the paths above will the rocket follow beyond point c?

B

A steel ball is attached to a string and is swung in a circular path in a horizontal plane as illustrated in the accompanying figure. At the point P indicated in the figure the string suddenly breaks near the ball. If these events are observed directly from above as in the figure, which path would the ball most closely follow after the string breaks?

B (diagonal)

The figure depicts a hockey puck sliding with constant speed vo in a straight line from point a to point b on a frictionless horizontal surface. Forces exerted by the air are negligible. You are looking down on the puck. When the puck reaches point b, it receives a swift horizontal kick in the direction of the heavy print arrow. Had the puck been at rest at point b, then the kick would have set the puck in horizontal motion with speed vk in the direction of the kick. Which of the paths above would the puck most closely follow after receiving the kick?

B (diagonal)

The figure shows a frictionless channel in the shape of a segment of a circle with its center at O. The channel has been anchored to a frictionless horizontal table top. Forces exerted by the air are negligible. You are looking down at the table. A ball is shot a high speed into the channel at p and exits at r. Which path in the figure below would the ball most closely follow after it exits the channel at r and moves across the frictionless table top?

B (straight up)

A bowling ball accidentally falls out of the cargo bay of an airliner as it flies along in a horizontal direction. As observed by a person standing on the ground and viewing the plane as in the figure, which path would the bowling ball most closely follow after leaving the airplane?

D

A rocket drifts sideways in outer space from point a to point b as shown in the figure. The rocket is subject to no outside forces. Starting at position b, the rocket's engine is turned on and produces a constant thrust (force on the rocket) at right angles to the line ab. The constant thrust is maintained until the rocket reaches a point c in space. Which of the paths below best represents the path of the rocket between points b and c?

E

The positions of two blocks at successive 0.20-second time intervals are represented by the numbered squares in the figure. The blocks are moving toward the right.

The acceleration of a equals the acceleration of b. Both accelerations are zero.

The positions of two blocks at successive 0.20-second time intervals are represented by the numbered squares in the figure. The blocks are moving toward the right. Do the blocks ever have the same speed?

Yes, at some time during the interval 3 to 4

The figure depicts a hockey puck sliding with constant speed vo in a straight line from point a to point b on a frictionless horizontal surface. Forces exerted by the air are negligible. You are looking down on the puck. When the puck reaches point b, it receives a swift horizontal kick in the direction of the heavy print arrow. Had the puck been at rest at point b, then the kick would have set the puck in horizontal motion with speed vk in the direction of the kick. Along the frictionless path you have chosen in question 8 (recall figure above), the main force(s) acting on the puck after receiving the kick is (are)

a downward force of gravity and an upward force exerted by the surface

The figure depicts a hockey puck sliding with constant speed vo in a straight line from point a to point b on a frictionless horizontal surface. Forces exerted by the air are negligible. You are looking down on the puck. When the puck reaches point b, it receives a swift horizontal kick in the direction of the heavy print arrow. Had the puck been at rest at point b, then the kick would have set the puck in horizontal motion with speed vk in the direction of the kick. The speed of the puck just after it receives the kick is:

greater than either of the speeds vo or vk, but less than the arithmetic sum of these two speeds

A woman exerts a constant horizontal force on a large box. As a result, the box moves across a horizontal floor at a constant speed vo. If the woman suddenly stops applying a horizontal force to the box, then the box will:

immediately start slowing to a stop.

The figure depicts a hockey puck sliding with constant speed vo in a straight line from point a to point b on a frictionless horizontal surface. Forces exerted by the air are negligible. You are looking down on the puck. When the puck reaches point b, it receives a swift horizontal kick in the direction of the heavy print arrow. Had the puck been at rest at point b, then the kick would have set the puck in horizontal motion with speed vk in the direction of the kick. Along the frictionless path you have chosen in question 8 (recall figure above), the speed of the puck after receiving the kick:

is constant

A large truck breaks down out on the road and receives a push back into town by a small compact car as shown in the figure. After the car reaches the constant cruising speed at which its driver wishes to push the truck:

the force of the car pushing on the truck equals the force of the truck pushing back on the car.

A large truck breaks down out on the road and receives a push back into town by a small compact car as shown in the figure. While the car is pushing the truck and speeding up to get to cruising speed:

the force of the car pushing on the truck equals the force of the truck pushing back on the car.

A large truck collides head-on with a small compact car. During the collision:

the truck exerts the same amount of force on the car as the car exerts on the truck.

An elevator is being lifted up an elevator shaft at a constant speed by a steel cable as shown in the figure. All frictional effects are negligible. In this situation, the forces on the elevator are such that:

the upward force by the cable equals the downward force of gravity.