How to Calculate Force and Acceleration: Elevator, Car, and Sailboat Examples

[kimikims]

A person weighting 0.6kN rides in an elevator that has a downward acceleration of 1.4m/s^2. The acceleration of gravity is 9.8 m/s^2. What is the magnitude of the force of the elevator floor on the person? Answer in units of kN.

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A 1317.9 kg car is coasting along a level road of 33 m/s. A constant breaking force is applied,such that the car is stopped in a distance of 63.7 m. What is the magnitude of the breaking force? Answer in units of N.

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A 12000 kg sailboat experiences an eastward force 28300 N due to the tide pushing its hull while the wind pushes the sails with a force of 75900 N directed toward the northwest (45 degrees westward of North or 45 degrees northward of West). What is the magnitude of the resultant acceleration of the sailboat? Answer in units of m/s^2.

What is the direction of the boats acceleration? Answer in units of degrees (N of West).


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I'm not sure what equations to use on these problems. Any help?

 

[photon_mass]

there are only 2 equations

 

[kimikims]

Well what 2 equations are those? I don't know what to use to solve these problems.

 

[In a "moment"um]

A person weighting 0.6kN rides in an elevator that has a downward acceleration of 1.4m/s^2. The acceleration of gravity is 9.8 m/s^2. What is the magnitude of the force of the elevator floor on the person? Answer in units of kN.

use F=ma

600 N=m 9.8 is how they arrived at the weight of a person. So the person weighed
600/9.8=m

the mass of the person is 61.2 kg

F=61.2kg*(9.8-1.4)

F=61.2kg *8.4 m/s sq
F=514.248 N
or 0.5 kN


The second one you need to a by using the formula V^2=V initial^2 + 2a(x1-x0)

0=V initial^2 +2a(63.7)

once you find a replace a in the formula F=ma

 

[kimikims]

A person weighting 0.6kN rides in an elevator that has a downward acceleration of 1.4m/s^2. The acceleration of gravity is 9.8 m/s^2. What is the magnitude of the force of the elevator floor on the person? Answer in units of kN.

use F=ma

600 N=m 9.8 is how they arrived at the weight of a person. So the person weighed
600/9.8=m

the mass of the person is 61.2 kg

F=61.2kg*(9.8-1.4)

F=61.2kg *8.4 m/s sq
F=514.248 N
or 0.5 kN


The second one you need to a by using the formula V^2=V initial^2 + 2a(x1-x0)

0=V initial^2 +2a(63.7)

once you find a replace a in the formula F=ma

0.5kN is wrong, is there a different way of solving this problem?

 

[Pyrrhus]

For the first problem use

Newton's 2nd Law

$$\sum_{i=1}^{n} \vec{F}_{i} = m \vec{a}$$

You got movement on the y-axis, the forces are the normal and the weight, the acceleration is downward. Use a free body diagram. Momentum's answer algebraically is correct, if you use webassign or similar try combinations of figures.

For the third problem

Remember

$$F = ma$$