Apparent Weight and Newtons Second law Problems

  • #1

Homework Statement



1. The first problem states that an elevator moves downwards with an acceleration of 3.36 m/s^2 with someone inside that has the mass of 64.2 kg. Now what is the apparent weight?

2. Blocks A and B are right next to each other. If 5.1 N were applied on block A, calculate the force block A applies onto block B assuming they stay next to each other the whole time. Block A is 3.1 kg and Block B is 5.3 kg. There is no friction involved.
A B
|////||/////|

3. Bob pushes a barrel that is 6.8kg 8.5m. He exerts 50N of force and the final velocity is 15 m/s, what is the initial force? No friction involved.

Homework Equations


1. m(g-a), not sure?

2. No idea

3. (F/m)- g = a plug a into another equation?

The Attempt at a Solution


1. 414.09 kg, not sure if right
2. No idea
3. Vi= 16.33 m/s, not sure if right
 

Answers and Replies

  • #2
71
0
you need to get into the habit of creating Free body diagrams to show all the forces on your system, these will help you understand the physics of more complex problems in the future.

1)
Force in Y = -mg - ma = - Weight

2) again sum the forces in the x direction
 
  • #3
I have no idea what you mean for 2), and for number 3 did I use the correct formula to account for gravity or am I supposed to leave gravity out?
 
  • #4
425
0
for 2)
what you gotta do is draw the FBD. It should contain the initial force applied in x direction and the contact force between the two blocks (say C).
Then plug in the equations using this basic relation F=m*a and solve the problem.
 
  • #5
The free body diagram is VERY IMPORTANT. It seems insignifigant but it is very useful. Before you can use any equations you have to add all of the forces on each axis. When you are done with that step you will have one NET force in the x direction and one NET force in the y direction. THEN you can go ahead and plug and chug.
 

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