Ch. 10 slides WorkEnergy.ppt

Work Questions Does K increase, decrease, or stay the same What is the sign of ∆K? What forces act on the object? For each of the forces that act on the object, is the work positive, negative or zero? Is Wnet positive, negative, or zero? Does this agree with ∆K? WorkEnergy.ppt

Pulling block A 10.2 kg box is pulled by a rope 1 meter along a rough horizontal surface (µk = 0.4). The rope is pulled with 100 Newtons so that it makes a 30° angle with the horizontal. The box starts at rest. Draw a free body diagram and compute the work done by each force, then find the net work. What is the final speed of the box? WorkEnergy.ppt

Block Up Ramp A 3 kg block slides up a frictionless ramp with an initial speed of 2 m/s. The ramp is inclined 30° from the horizontal. How high will the block slide? How far up the incline will the block slide? If the ramp is inclined at a 60° angle, will your answers to a) and b) change? Energy.ppt

Block into Spring A block sliding along a frictionless horizontal surface with velocity v collides with and compresses a spring. The maximum compressions is 1.4 cm. If the block then collides with the spring while having velocity 2v, the spring’s maximum compression will be a) 0.35 cm b) 0.7 cm c) 1.0 cm d) 1.4 cm e) 2.0 cm f) 2.8 cm g) 5.6 cm Energy.ppt

Shooting Block A 1-m tall spring with spring constant 50,000 N/m is placed vertically on the ground. A 1 kg block is placed on the spring after the spring is compressed 20 cm. The spring is released and the block is launched into the air. Draw an energy bar chart at while the spring is compressed, just after the block is launched, and when the block reaches its maximum height. Find the maximum height of the block. Find the speed of the block just after it loses contact with the spring. Energy.ppt

Bobsled The next Olympic games will have a new bobsledding event. A person will run a distance of 100 m with a very light sled and then slide down a 20 m track sloped at 30° into a spring of length 5 m and a spring constant of 4000 N/m. The person who compresses the spring the farthest wins the gold medal. Julia (m = 50 kg) compresses the spring 2 m. What was Julia’s maximum running speed? Assume the track is frictionless. The Olympic steering committee has exact specifications for the design of the track. Is this really necessary? In other words, is the shape of the track important? If not, what is important? Energy.ppt

Shuffleboard You’ve designed a shuffleboard-type game where a compressed spring pushes a weighted disc across a floor. The amount you compress the spring will determine how far it travels. A disc of mass 1kg is compressed 10 cm against a spring with spring constant k = 500 N/m. It is pushed along a floor with a kinetic coefficient of friction of 0.25 with the block. What forms of energy are in this system? What’s the disc’s speed when it leaves the spring? How far does it travel from its starting position? WorkEnergy.ppt

Block A block of mass 1000-kg is compressed 10 m against a spring with spring constant k = 1000 N/m. The block follows the curve shown below. The track is frictionless, but the incline at the end of the track has coefficients of friction µs = 0.5 and µk = 0.25 (fk=1877 N). The incline makes a 40° with the horizontal and H = 10 m. C A B How far up the incline does the block slide? What is the speed of the block at point B? WorkEnergy.ppt

Pulling block A 100 g rock is placed into a 10-cm elastic sling shot that has a spring constant of 5000 N/m. The sling shot is stretched 10 cm and then released so that the rock is launched at an angle of 50°. WorkEnergy.ppt

Inelastic Collisions A 500 g cart moving at 2 m/s collides and sticks to a 2 kg cart at rest. What is the final speed of the two carts? Is mechanical energy conserved in this collision?

Ballistic Spring A 5-gram bullet moving with an initial speed of 500 m/s gets embedded into a 2-kg wood block. The wood block, initially at rest, sits against a spring of force constant 400 N/m and moves on a frictionless horizontal surface. What is the maximum compression of the spring? Is Mechanical Energy conserved?