Simple Work problem with block and friction.

So after calculating the vertical component (400*sin(20)=136.2N) we get a net force of 5638.2J - 136.2*15= 3438.2J.In summary, the net work done on the block after being pulled 15 meters is 3438.2J.
  • #1
TwinGemini14
34
0
Suppose that a 50kg block slides along a horizontal surface where the coefficient of kinetic friction between the block and the surface is 0.60. A force F = 400 N is now applied where the angle of the force above horizontal is 20°. (Like a string pulling the block from the right 20 degrees above the horizontal)

What is the net work done on the block after the block is pulled 15 meters?

A) 1.54 * 10^3 J
B) 2.45 * 10^3 J
C) 2.75 * 10^3 J
D) 3.00 * 10^3 J
E) 3.29 * 10^3 J

----

The force applied across the horizontal is Fcos(20) = 400*cos(20) = 375.88N.
The frictional force opposing this is (0.6)(50)(-9.8) = -294N.

So the work done by the applied force is W = Fd = (375.88)(15) = 5638.2J.
The work done by the frictional force is W = Fd = (-294)(15) = -4410J.

The net force is then... W = (5638.2)+(-4410) = 1228.2J.

I got 1.23 * 10^3J ... but that is not a choice. Where did I go wrong? Can anybody help me out here?
 
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  • #2
You have to take the vertical component of the force, which reduces the weight of the block, and hence the frictional froce.
 
  • #3


I would first check the units of the final answer to make sure they match the given answer choices. In this case, the correct answer is A) 1.54 * 10^3 J, which is equivalent to 1540 J. So it appears that your calculation is correct, but you may have made a mistake in converting units or rounding your answer. It is also possible that there is a typo in the given answer choices. I would recommend double checking your calculations and units to ensure accuracy. If you are still unsure, you can always seek help from a colleague or a tutor.
 

Related to Simple Work problem with block and friction.

1. What is a work problem with block and friction?

A work problem with block and friction is a physics problem that involves calculating the amount of work done when an object is moved along a surface with friction. It takes into account the force applied, the displacement of the object, and the coefficient of friction between the object and the surface it is moving on.

2. How do you calculate work in a problem with block and friction?

To calculate work in a problem with block and friction, you need to use the formula W = Fd cosθ, where W is work, F is the force applied, d is the displacement, and θ is the angle between the force and displacement vectors. You also need to consider the coefficient of friction and any other external forces that may affect the block's movement.

3. What is the role of friction in a work problem with block and friction?

Friction plays a crucial role in a work problem with block and friction because it is the force that opposes the motion of the block. The coefficient of friction determines how much force is needed to overcome friction and move the block. Without friction, the block would continue to move at a constant speed with no work being done.

4. How does the angle of the surface affect the work done in a problem with block and friction?

The angle of the surface affects the work done in a problem with block and friction because it determines the angle between the force and displacement vectors. When the surface is horizontal, the angle is 0 and the work is equal to the force multiplied by the displacement. As the angle increases, the work decreases because the cosine of the angle decreases.

5. What are some real-life examples of work problems with block and friction?

Some real-life examples of work problems with block and friction include pushing a box across the floor, pulling a suitcase along the ground, and sliding a book across a desk. These situations all involve a force being applied to an object that is moving along a surface with friction, and the work done can be calculated using the formula W = Fd cosθ.

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