Learning Goal: To understand the relationship between applied force, net force,

Question

Learning Goal:

To understand the relationship between applied force, net force, acceleration, and mass for 1-dimensional motion.

For this problem, use the PhET simulation Forces and Motion: Basics. This simulation allows you to push on different objects with a certain horizontal force and see the resulting motion. You can control the mass of the objectby using different objects or by stacking up to three objects on top of one another. Click and drag on the objects to move them to the desired location. You can also adjust Friction between None and Lots by using the slider provided on the right side of the window.

While the object is being pushed, you can see the directions and values of the various horizontal forces acting on it, as well as the value of the sum of these forces. In addition you can display the mass, speed, and acceleration of the object.

Start the simulation. When you click the simulation link, a new window will open. Double-click on Acceleration to get started.

Adjust the Applied Force by moving the slider bar (which is at the center bottom of the main window) left or right. Release the slider to stop applying a force on the object. You can also adjust the Applied Force in increments of 50 Newtons by clicking on the left and right arrows above the slider bar. Apply a force on the crate and watch the resulting motion.

Feel free to play around with the simulation, and investigate what happens when you click on either the figure or the object, while they are in motion. When you are done, hit reset (round button with a circular arrow, to the right) and set Friction to None prior to beginning Part A. Make sure that Forces, Sum of Forces, Values, Masses , Speed, and Acceleration are all selected

Choose the 200 kg refrigerator. Set the applied force to 400 N (to the right). Be sure friction is turned off.
What is the net force acting on the refrigerator?

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Correct

Since there is no friction, the only horizontal force is due to the applied force. The normal force (directed upward) and the force of gravity (directed downward) exactly cancel out.

Part B

Part complete

What is the acceleration a of the refrigerator 4 s after the person begins pushing on it with a force of 400 N?

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Applying Newton’s 2nd law, a=Fnet/m=(400N)/(200kg)=2m/s2. The acceleration is constant.

Part C

Part complete

Adjust the mass of the refrigerator by stacking different objects on top of it.
If the mass of the refrigerator is increased (with the Applied Force held constant), what happens to the acceleration?

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Since Fnet=ma, the acceleration is inversely proportional to the mass.

Part D

Part complete

Click the reset button, and adjust the Friction back to None.With the 50kg crate selected, use the slider to apply a force of about 100N. After 3 s have elapsed, release the slider so that the Applied Forceis now zero, and the figure is standing still. What happens to the crate after the Applied Force (force exerted) goes to zero?

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Because the friction is turned off, there are no horizontal forces acting on the crate if the applied force is set to zero. This means that the acceleration must be zero, causing the velocity to remain constant. The cratea never slows down or stops!

Part E

Part complete

Click on the crate to bring it to a stop, then replace it with the refrigerator. Use the slider to apply a force of about 400 N. After2 s have elapsed in the simulation, decrease the Applied Force (force exerted) slowly back to zero. Try to do this adjustment in roughly 2 s . While the Applied Force (force exerted) is decreasing, the velocity is

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Even though the acceleration is decreasing as the applied force is decreasing, the acceleration is still positive, so the velocity must still be increasing. A smaller acceleration causes the rate of change of the velocity to decrease. You should see this on the Speed indicator; as the acceleration goes down, the needle rotates more slowly.

Part F

Part complete

Click on the reset button, and stack one 50kg. crate on top of the other, so that the total mass is 100kg. The Friction should be set to halfway between None and Lots. Adjust the Applied Force (force exerted) slowly, and determine when the crates begin accelerating. What is the minimum force that must be exerted on the crates so that they accelerate?

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The maximum force of static friction is given by fmax=?mg, where ? is the coefficient of static friction, m is the mass, and g is the acceleration due to gravity. The force of static friction will be exactly equal to the applied force up to this amount. If the applied force is greater than this amount, the crates accelerate.

Part G

Part complete

If the Applied Force (force exerted) on both crates with the current Friction setting is 350N,, the acceleration is

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The net force on the crates is Fnet=(350?250)N=100N, so the acceleration is a=100N/(100kg)=1m/s2. This acceleration is constant in time since the force of friction does not depend on the velocity.

I NEED THIS QUESTION Q: Click the reset button, and set the Applied Force (force exerted) to 350 N . After about 3 s , set the Applied Force back to zero. After the applied force (force exerted) is turned off, what happens to the crate?

The magnitude of the net force is 400N, directed to the right. The net force is zero. The magnitude of the net force is greater than 400N, directed downward and to the right. The magnitude of the net force is less than 400N, directed to the right. The magnitude of the net force is greater than 400N, directed upward and to the right. Forces Speed Sum of Forces Values Masses Speed Acceleration- Sum of Friction Lots None pplied Force 0 Newtons | 500 500 Forces and Motion: Basics Net ForceMobo Acceeraton

Explanation / Answer

Q. If the applied force is turned off after 3s then after moving for some time the crate will come to rest due to frictional force which acts in oppossite direction to the motion of the crate. The velocity of the crate after 3s is 3m/s. The deceleration of the crate is = (250/100)=2.5m/s^2. Thus the crate will remain in motion for (3/2.5)s=1.2s. After that crate will come to rest

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