# work and energy

1. ### A Motorcyclist crossing a stretch of land

TA = Ec 0,7*m*g*d = (m*v² /2) 1,4*g*d = (400/12,96) 14*d = (400/12,96) d = 2,2 m No
2. ### Work and energy of an object on a ice slope

Homework Statement: A perfect hemisphere of frictionless ice has radius R=7 meters. Sitting on the top of the ice, motionless, is a box of mass m=7 kg. The box starts to slide to the right, down the sloping surface of the ice. After it has moved by an angle 11 degrees from the top, how much...
3. ### Work of a object moving across surfaces with different friction

Homework Statement: Hetsut is the foreman of a construction project in ancient Egypt. He needs to move a giant block of stone, of mass 12 metric tons, from the docks to the temple grounds. He can go along the roads by travelling 295 meters east, then 89 meters north. Along the roads, the...
4. ### Work of gravity on an object sliding down a frictionless sphere

Homework Statement: A perfect hemisphere of frictionless ice has radius R=6.5 meters. Sitting on the top of the ice, motionless, is a box of mass m=6 kg. The box starts to slide to the right, down the sloping surface of the ice. After it has moved by an angle 20 degrees from the top, how much...
5. ### Total work of a directional wind on a mailman

Homework Statement: Mike the Mailman takes his oath seriously: "Neither snow, nor rain, nor heat, nor gloom of night stays these courageous couriers from the swift completion of their appointed rounds". Even though a blizzard is raging outside, he goes out to deliver the mail. He makes four...
6. ### Work required to attach the bowstring to the bow?

E final = (1/2)(500)(1.14012)^2 = 324.968 J E initial = (1/2)(500)(0.5)^2 = 62.5 J E final - E initial = 262.468 J
7. ### Classical Mechanics Problem Based On Conservation Of Energy

I have tried using Conservation of Energy but I'm getting incorrect answer.
8. ### Inelastic collision problem: Bullet striking a wood block

Hey everyone I'm struggling on the last part of this assignment. I need to find the total work done by the block and the bullet, when the collision happens. The informations is: mblock=0.3 kg mbullet=0.01 kg vg=700 m/s Height=0.72m The final speed after the collision is vf=22.6 m/s and the...
9. ### Water Tank Refilling via Hydraulic Water Pumping System

Based on my understanding, Top Tank Refilling Advantage: Atmospheric Pressure Disadvantage: High Head (Requires more distance, thus more Work since W = f x d) Bottom Tank Refilling Advantage: Low Head Disadvantage: High Static Pressure (Requires more Force, thus more Work since W = f x d)...
10. ### What is the kinetic energy of the block when it is moved 2cm.

My attempt at the solution... I only have problem in solving part a) 1) i calculated the spring force actingbon the table block and it is greater than the frictionnand tension force acting in the opposite direction, so by that the block will move in left. 2) now i found that which forces are...
11. ### B Why there is a negative sign in the formula of calculating work done?

$$W = - \int _ { a } ^ { b } \vec { F } \cdot d \vec { r }$$ ( The Force here is referring to the applied force, When moving a positive charge towards another positive charge(stationary) / field In this formula why there is a negative sign in the formula? I am not asking the sign of the total...
12. ### What is the direction of work in this figure?

iam not sure of the direction of work , is it positive becouse pulleys change the direction of the force ? or is it negative because of the arrow that indicates the direction of acceleration ??!
13. ### I Work done on an object given a variable mass

I was just doing some review on my physics lecture and I stumble on the idea of what if there was an object hanging and the cord mass is also included in the weight and it's displaced upward without having velocity nor time hypothetically and the cord change mass. I tried solving it by W = fΔx...
14. ### Calculate the impact force when falling from a height

To find vx vx = dx/t = 3.86 m/1.5 s= 2.573 m/s To find Ek Ek = ½mvx²= ½(79.4)(2.573)²= 262.8 J W = FnetΔd Fnet = 262.8 J/ 3.86 m = 68 N He hits him with a force of 68N
15. ### Maximum displacement in mass spring system

1. Homework Statement A block is suspended by an ideal spring of the force constant K. If the block is pulled down by applying a constant force F and if maximum displacement of the block from its initial position of rest is X then, find the value of X. 2. Homework Equations mg + F = XK +...
16. ### What is the work done on cart by the string?

1. Homework Statement A cart of mass M1 = 6 kg is attached to a block of mass M2 = 3 kg by a string that passes over a frictionless pulley. The system is initially at rest and the table is frictionless. After the block has fallen a distance h = 1 m: What is the work Ws done on the cart by the...
17. ### Shooting bullets, work & power

1. Homework Statement When bullets are shot on Superman, they bounce off of his chest. 100 Bullets will be shot on his chest per minute, each with a mass of 9g and v= 1000m/s. Assume that the bullets will bounce off elastically back in x-direction. a) What is the average power of all of the...
18. ### Kinetic energy & Conservation of energy

1. Homework Statement You are driving with your car (of total mass: 1.2tonnes) with a speed of v=50km/h, until you see an obstacle. a) What is the kinetic energy of the car? b) When you start to brake, there is still 15m until the obstacle. What must be the size of the friction coefficient...
19. ### Finding the Work of a spring and friction with a changing angle

1. Homework Statement We shot a projectile with mass $m$ and velocity $v_0$ with angle $\phi$ it collide with a box with mass $M$ at the maximum height of its path. Then, they both start to move with another speed. (We define $t=0$ at this time) (Completely Inelastic Collision). The...
20. ### Question about the Work-Kinetic Energy Theorem - Pulling a cart

1. Homework Statement Question from Fundamentals of Physics (Halliday, Resnick, Walker) This figure below shows a cord attached to a cart that can slide along a frictionless horizontal rail aligned along an x axis. The left end of the cord is pulled over a pulley, of negligible mass and...
21. ### Problem in understaning potential energy

1. Homework Statement If we lift a block with constant velocity, by applying a force mg upwards, is the work done zero? 2. Homework Equations 3. The Attempt at a Solution The work done must be zero as the resultant force is zero, what I don't understand is how does the block get potential...
22. ### I Pendulum: Calculating Work

I know that I'm rushing too much but I wanted to see if I can calculate the work of a pendulum that does oscillation with a similar way you calculate the work of a spring. Consider the following free body diagram: Things i noticed: 1) The position is changing both in x and y axis while the...
23. ### Work: I am having problem determining the elongation in spring

1. Homework Statement A spring has been attached to an object which is kept on the ground. The spring is initially in its natural length: 'l' when a force 'F' is applied on it. The force 'F' slowly pulls the object so it does not attain any acceleration. There's a point 'P' on the line which...
24. ### How could the block A move to the left corner?

1. Homework Statement See question number 5. 2. Homework Equations F=m*a W=F*s Uniform acceleration motion equations 3. The Attempt at a Solution Actually,I am having some difficult understanding the problem. See the F.B.D of the system, see the friction is acting on the block in the...
25. ### B Work Lifting Things With and Without Torque

If I lift a 1kg broom stick 1m when holding it from its center of mass, I will have done 9.8J of work and the broomstick would have gained 9.8J of potential energy. If I were instead to lift it from one end I would have to exert a much larger force due to torque. Lifting this same 1kg broomstick...
26. ### Problem in calculating work done?

1. Homework Statement See question number 3 2. Homework Equations Work Done="integral" F*ds 3. The Attempt at a Solution I tried to solve this question using integration, I have replaced F with "1" and ds with "t^2+2t". So I am stuck in at that step. Please help me differentiate it...
27. ### Hi, help me to check my answers, dynamics, energy and work

1. Homework Statement Whats is the final speed of the second box(mass = 1kg) when the first one (mass = 5 kg) has descended a distance equal to 0.6 meters in the rough ramp inclined 60° respect the x axis. Consider the spring is compressed a length x = 0.2 meters. The second box is tied to the...
28. ### Problem with solving for force constant k of spring?

The question is stated as the following: When a 3.60 kg object is placed on top of a vertical spring, the spring compresses a distance of 2.83 cm. What is the force constant of the spring? The correct answer was acquired by using the equation F = mg = -kx, where k is the spring constant and x...
29. ### Not sure how to plug in numbers for Work Energy Theorem

1. The Problem Stament, all variables and given data a 15 kg crate, initially at rest, slides down a ramp 2.0 m long and inclined at an angle of 20 degrees with the horizontal. if there is a constant force of kinetic friction of 25 N between the crate and ramp, what kinetic energy would the...
30. ### Finding the Kinetic Energy using the mass, radius and initial KE

Information Given:Zero, a hypothetical planet, has a mass of 4.2 x 1023 kg, a radius of 2.8 x 106 m, and no atmosphere. A 10 kg space probe is to be launched vertically from its surface. Question: (a) If the probe is launched with an initial kinetic energy of 5.0 x 107 J, what will be its...