Applying Newtons Second Law to Vertical Motion

This is not the answer to the original question, which asked for what force the cable exerts to give the car its acceleration.
  • #1
Ahmad786
17
0
18. An elevator that weighs 3.5 x 103 N is accelerated upward at 1.0 m/s2. What force does the cable exert to give it this acceleration?
A. 357 N
B. 0 N
C. 3500 N
D. 3857 N
(For this quesion I was really confused and I guessed that the force of tension in the cable was what the cable weighed )
Is that answer correct if not how do I find the correct answer?
 
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  • #2
Ahmad786 said:
(For this quesion I was really confused and I guessed that the force of tension in the cable was what the cable weighed )


This would only be true if the forces on the elevator car were balanced. However, since the elevator car has a non-zero acceleration, Newton's Second Law tells you that the forces on the elevator car are NOT balanced i.e. there is a net force acting. Hint: you can use Newton's Second Law to calculate the net force from the mass and acceleration, and then use the result to figure out how the tension compares to the weight.

Draw a free body diagram: it will help you immensely.
 
  • #3
"What force does the cable exert to give it this acceleration?" is this asking for net force if it is could I use the equation Fnet=Ft+Fg and If I used this Would it look like this?:
Fnet=Ft+Fg Fnet=(3500N/9.81m/s2)(1.00m/s2)+3500N so would the answer be D. 3857 N
 
  • #4
The car has two forces acting on it. Tension upward, and weight downward. The fact that the car is accelerating upward tells you that the tension must be greater than the weight (in magnitude). The net force is of course just the difference between the two (in other words, it is the amount by which the tension is greater than the weight). Therefore, your answer is correct, but your labelling of quantities is wrong. You are calculating Ft, not Fnet, using the formula:

Fnet = Ft - Fg

which implies: Ft = Fnet + Fg

which is the calculation you did, leading to an answer of D (for Ft).
 

1. How does Newton's Second Law apply to vertical motion?

According to Newton's Second Law, the force applied to an object is equal to its mass multiplied by its acceleration. In the case of vertical motion, the force acting on an object is its weight (mass multiplied by gravity) and the acceleration is determined by the influence of other forces, such as air resistance or friction.

2. What is the equation for calculating the net force in vertical motion?

The equation for calculating the net force in vertical motion is Fnet = ma, where Fnet is the net force, m is the mass of the object, and a is the acceleration.

3. How does the direction of the net force affect the vertical motion of an object?

The direction of the net force affects the vertical motion of an object by determining the direction of the acceleration. If the net force is upward, the object's acceleration will be upward, causing it to move in the positive direction. If the net force is downward, the object's acceleration will be downward, causing it to move in the negative direction.

4. What happens to the acceleration of an object in free fall?

In free fall, an object is only influenced by its weight and experiences no air resistance. This means that the net force is equal to the weight of the object, and thus, the acceleration of the object is constant. In most cases, the acceleration due to gravity is used, which is approximately 9.8 m/s^2.

5. How can Newton's Second Law be applied to calculate the velocity of an object in vertical motion?

By using the equation v = u + at, where v is the final velocity, u is the initial velocity (usually 0 in free fall), a is the acceleration, and t is the time, we can calculate the velocity of an object in vertical motion. This equation is derived from Newton's Second Law, as the net force causes the object to accelerate and change its velocity over time.

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