Force Concept Questionspeppardcrphysics.weebly.com/uploads/3/0/4/3/30435144/force_conc… · is Newton’s 3rd Law!! But the acceleration is F/m and so the smaller mass has the bigger

Force clicker questions.notebook

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November 29, 2017

Oct 297:57 AM

Force Concept Questions

Grade:«grade»Subject:«subject»

Date:«date»

Oct 297:59 AM

1 A book is at rest on a table. The book will remain there because...

A there is a net force on the book, but it has too much inertia

B there are no forces acting on the boook

C it moves but too slowly to be seen

D there is no net force on the book


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November 29, 2017

Oct 297:38 AM

D

There are forces acting on the book, but the only forces acting are in the ydirection. Gravity acts downward, but the table exerts an upward force that is equally strong, so the two forces cancel, leaving no net force.

Oct 298:02 AM

1 A puck slides on ice at a constant velocity. What is the net force acting on the puck?

A more than mg

B equal to mg

C less than mg but greater than zero

D zero


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November 29, 2017

Oct 297:38 AM

D

The puck is moving at a constant velocity, and therefore it is not accelerating. Thus, there must be no net force acting on the puck.

Followup: Are there any forces acting on the puck? What are they?

Oct 298:06 AM

2 You put your book on the bus seat next to you. When the bus stops suddenly, the book slides forward off the seat. Why?

A a net force acted on it

B no net force acted

C it did not move but only seemed to move

D gravity briefly stopped acting on it


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November 29, 2017

Oct 297:38 AM

B

The book was initially moving forward (since it was on a moving bus). When the bus stopped, the book continued moving forward, which was its initial state of motion, and therefore it slid forward off the seat.

Oct 298:10 AM

3 You kick a smooth flat stone out on a frozen pond. The stone slides, slows down and eventually stops. You conclude that:

A The pushing force stopped

B no net force acted

C a net force acted

D it has a natral tendency to be at rest


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November 29, 2017

Oct 297:38 AM

C

After the stone was kicked, no force was pushing it along! However, there must have been some force acting on the stone to slow it down and stop it. This would be friction!!

Followup: What would you have to do to keep the stone moving?

Oct 298:13 AM

4 A very large truck sits on a frozen lake. Assume there is no friction between the tires and the ice. A fly suddenly smashes against the front window. What will happen to the truck after the fly stops moving?

A its too heavy, so it jst sits there

B it moves backward with a constant speed

C it moves forward with a constant speed

D it falls through the ice


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November 29, 2017

Oct 297:38 AM

B

When the fly hit the truck, it exerted a force on the truck (only for a fraction of a second). So, in this time period, the truck accelerated (backwards) up to some speed. After the fly was squashed, it no longer exerted a force, and the truck simply continued moving at constant speed.

Oct 298:16 AM

5 From rest, we step on the gas of our Ferrari, providing a force F for 4 secs, speeding it up to a final speed v. If the applied force were only 1/2 F, how long would it have to be applied to reach the same final speed?

A 16 s

B 8 s

C 4 s

D 2 s


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November 29, 2017

Oct 297:38 AM

B

In the first case, the acceleration acts over time T = 4 s to give velocity v = aT. In the second case, the force is half, therefore the acceleration is also half, so to achieve the same final speed, the time must be doubled.

Oct 298:21 AM

6 A force F acts on mass M for a time interval T, giving it a final speed v. If the same force acts for the same time on a different mass 2M, what would be the final speed of the bigger mass?

A 2v

B v

C 1/2 v

D 1/4 v


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November 29, 2017

Oct 297:38 AM

B

In the first case, the acceleration acts over time T to give velocity v = aT. In the second case, the mass is doubled, so the acceleration is cut in half, therefore, in the same time T, the final speed will only be half as much.

Oct 298:27 AM

7 A force F acts on mass m1 giving acceleration a1. The same force acts on a different mass m2 giving acceleration a2 = 2a1. If m1 and m2 are glued together and the same force F acts on this combination, what is the resulting acceleration closest to?

A .75 a1.

B 1.5 a1.

C .5 a1.

D .66666 a1.


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November 29, 2017

Oct 297:38 AM

D

Mass m2 must be (1/2)m1 because its acceleration was 2a1 with the same force. Adding the two masses together gives (3/2)m1, leading to an acceleration of (2/3)a1 for the same applied force.

Oct 298:32 AM

8 What can you say about the force of gravity Fg acting on a stone and a feather?

A Fg is greater on feather

B Fg is greater on stone

C Fg is same for each

D Fg is zero because of evacated tube


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November 29, 2017

Oct 297:38 AM

B

The force of gravity (weight) depends on the mass of the object!! The stone has more mass, therefore more weight.

Oct 298:34 AM

9 What can you say about the acceleration of gravity acting on the stone and the feather?

A it is greater on feather

B it is greater on stone

C it is equal on both

D it is zero becase of evacuated tube


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November 29, 2017

Oct 297:38 AM

C

The acceleration is given by F/m so here the mass divides out. Since we know that the force of gravity (weight) is mg, then we end up with acceleration g for both objects.

Oct 298:37 AM

10 A block of mass m rests on the floor of an elevator that is moving upward at constant speed. What is the relationship between the force due to gravity and the normal force on the block?

A N > mg

B N = mg

C N < mg

D N = 0

m

v


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November 29, 2017

Oct 297:38 AM

B

The block is moving at constant speed, so it must have no net force on it. The forces on it are N (up) and mg (down), so N = mg, just like the block at rest on a table.

Oct 298:40 AM

11 A block of mass m rests on the floor of an elevator that is accelerating upward. What is the relationship between the force due to gravity and the normal force on the block?

A N > mg

B N = mg

C N <mg but non zero

D N = 0


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November 29, 2017

Oct 297:38 AM

A

The block is accelerating upward, so it must have a net upward force. The forces on it are N (up) and mg (down), so N must be greater than mg in order to give the net upward force!

Σ F = N – mg = ma > 0 ∴ N > mg

Followup: What is the normal force if the elevator is in free fall downward?

Oct 298:42 AM

12 Below you see two cases: a physics student pulling or pushing a sled with a force F which is applied at an angle θ. In which case is the normal force greater?

A 1

B 2

C same

D depends on magnitde of F

Case 1

Case 2


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November 29, 2017

Oct 297:38 AM

A

In Case 1, the force F is pushing down (in addition to mg), so the normal force needs to be larger. In Case 2, the force F is pulling up, against gravity, so the normal force is lessened.

Case 1

Case 2

Oct 298:45 AM

13 Consider two identical blocks, one resting on a flat surface, and the other resting on an incline. For which case is the normal force greater?

A A

B B

C Same

D Can't tell

A B


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November 29, 2017

Oct 297:38 AM

θ

A

Case A, we know that N = mg. In Case B, due to the angle of the incline, N < mg. In fact, we can see that N = mg cos(θ).

Oct 298:48 AM

14 In outer space, a bowling ball and a pingpong ball attract each other due to gravitational forces. How do the magnitudes of these attractive forces compare?A Bowling ball exerts greater force

B Ping Pong ball exerts greater force

C forces are equal

D forces are zero


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November 29, 2017

Oct 298:51 AM

F12 F21

C

The forces are equal and opposite by Newton’s 3rd Law!

Oct 298:55 AM

15 In outer space, gravitational forces exerted by a bowling ball and a pingpong ball on each other are equal and opposite. How do their accelerations compare?

A accelerations are equal but not opposite

B accelerations are opposite, but bigger for bowling ball

C accelerations are opposite, but bigger for ping pong ball

D accelerations are equal and opposite


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November 29, 2017

Oct 297:38 AM

C

The forces are equal and opposite this is Newton’s 3rd Law!! But the acceleration is F/m and so the smaller mass has the bigger acceleration.

Followup: Where will the balls meet if they are released from this position?

Oct 2911:53 AM

16 A small car collides with a large truck. Which experiences the greater impact force?

A car

B truck

C same

D it depends on the velocity of each


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November 29, 2017

Oct 297:38 AM

C

According to Newton’s 3rd Law, both vehicles experience the same magnitude of force.

Nov 296:57 AM

Force Concept Questionspeppardcrphysics.weebly.com/uploads/3/0/4/3/30435144/force_conc… · is Newton’s 3rd Law!! But the acceleration is F/m and so the smaller mass has the bigger

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