Applying Newton's laws

In summary: The total force is the applied force minus the retarding force (the friction is not relevant for this problem). The mass is given. You will need the acceleration to get the distance the mower moves in 2 seconds. (Hint: There is a kinematics formula for this.)
  • #1
kgood5885
2
0
A person pushes a 13.0 kg lawn mower at constant speed with a force of 84.0 N directed along the handle, which is at an angle of = 49.0° to the horizontal.

(a) Calculate the horizontal retarding force on the mower

(b) Calculate the normal force exerted vertically upward on the mower by the ground.

(c) Calculate the force the person must exert on the lawn mower to accelerate it from rest to 1.3 m/s in 2.0 seconds (assuming the same retarding force).

Here's what I have so far...

a) FPx = 84 cos 49 = 55.11 N
FPy = 84 sin 49 = 63.396 N
∑ F = ma
N – mg = ma
N = mg
= 13.0(9.8)
= 127.4 N

b) Ffr = (coefficient of friction)FN
= (0.30)(127.4)
= 38.22 N
c) I have no idea where to even start for this question!

Please help!
 
Physics news on Phys.org
  • #2
kgood5885 said:
Here's what I have so far...

a) FPx = 84 cos 49 = 55.11 N
FPy = 84 sin 49 = 63.396 N
∑ F = ma
N – mg = ma
N = mg
= 13.0(9.8)
= 127.4 N
All you need to answer this part is to realize that the net horizontal force must be zero. The retarding force must balance the horizontal component of the applied force.

b) Ffr = (coefficient of friction)FN
= (0.30)(127.4)
= 38.22 N
For this part, all you need to find is the normal force. (Where did you get the coefficient of friction?) This time use the fact that the net vertical force must be zero. (Hint: There are three vertical forces.)
c) I have no idea where to even start for this question!
To get an acceleration, the net horizontal force must be greater than zero. Apply Newton's 2nd law.
 
  • #3


I would like to commend you on your calculations so far. You have correctly applied Newton's laws to determine the retarding force and normal force on the lawn mower. To calculate the force required to accelerate the lawn mower, we can use the equation F = ma, where F is the net force, m is the mass, and a is the acceleration. In this case, we know the mass of the lawn mower (13.0 kg) and the acceleration (1.3 m/s^2), so we can rearrange the equation to solve for the net force, which is the force that the person must exert on the lawn mower.

F = ma
F = (13.0 kg)(1.3 m/s^2)
F = 16.9 N

Therefore, the person must exert a force of 16.9 N on the lawn mower to accelerate it from rest to 1.3 m/s in 2.0 seconds, assuming the same retarding force of 38.22 N. This means that the person must push with a force of 16.9 N plus the retarding force of 38.22 N, for a total force of 55.11 N, in order to achieve this acceleration.

In summary, by applying Newton's laws, we can determine the retarding force and normal force on the lawn mower, as well as the force required to accelerate it. These calculations are essential for understanding the motion and forces involved in this scenario.
 

1. What are Newton's three laws of motion?

Newton's first law states that an object will remain at rest or in motion with a constant velocity unless acted upon by an external force. Newton's second law states that the acceleration of an object is directly proportional to the net force applied to it and inversely proportional to its mass. Newton's third law states that for every action, there is an equal and opposite reaction.

2. How do Newton's laws apply to everyday life?

Newton's laws can be observed in many everyday situations, such as pushing a shopping cart (demonstrating the first law), throwing a ball (demonstrating the second law), and riding a skateboard (demonstrating the third law).

3. What is the difference between weight and mass according to Newton's laws?

Mass is a measure of the amount of matter in an object, while weight is a measure of the force of gravity acting on an object. According to Newton's second law, an object's weight is directly proportional to its mass and the acceleration due to gravity.

4. How do Newton's laws relate to the concept of inertia?

Newton's first law, also known as the law of inertia, states that an object will remain at rest or in motion unless acted upon by an external force. This concept of inertia is directly related to Newton's first law and is the reason why objects tend to resist changes in their state of motion.

5. How do we apply Newton's laws in engineering and design?

Engineers and designers use Newton's laws to understand and predict the behavior of objects and systems. For example, they use Newton's second law to calculate the forces acting on structures and machines, and Newton's third law to design efficient propulsion systems for vehicles.

Similar threads

  • Introductory Physics Homework Help
Replies
13
Views
857
  • Introductory Physics Homework Help
Replies
17
Views
517
  • Introductory Physics Homework Help
Replies
5
Views
1K
  • Introductory Physics Homework Help
Replies
9
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
315
  • Introductory Physics Homework Help
Replies
33
Views
2K
  • Introductory Physics Homework Help
Replies
4
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
1
Views
643
  • Introductory Physics Homework Help
Replies
6
Views
5K
Back
Top