Exam 6: Work and Energy

A force acts on an object, causing it to move parallel to the force. The graph in the figure shows this force as a function of the position of the object. How much work does the force do as the object moves from 0 m to 4 m?

Two objects, one of mass m and the other of mas $2 m$ are dropped from the top of a building. If there is no air resistance, when they hit the ground

How much work is required to stretch an ideal spring of spring constant (force constant) 40 N/m from x=0.20 m to x=0.25 m if the unstretched position is at x=0.00 m?

A truck has four times the mass of a car and is moving with twice the speed of the car. If $K _ { \mathrm { t } } \text { and } K _ { \mathrm { c } }$ refer to the kinetic energies of truck and car respectively, it is correct to say that

A 1000-kg car experiences a net force of 9500 N while slowing down from 30 m/s to 15.9 m/s. How far does it travel while slowing down?

Joe and Bill throw identical balls vertically upward. Joe throws his ball with an initial speed twice as high as Bill. If there is no air resistance, the maximum height of Joe's ball will be

A heavy sled and a light sled, both moving horizontally with the same kinetic energy, suddenly slide onto a rough patch of snow and eventually come to a stop. The coefficient of kinetic friction Between the sleds and the rough snow is the same for both of them. Which of the following Statements about these sleds are correct? (There could be more than one correct choice.)

On a planet where g = 10.0 m/s² and air resistance is negligible, a sled is at rest on a rough inclined hill rising at 30° as shown in the figure. The object is allowed to move and it stops on a rough Horizontal surface, at a distance of 4.0 m from the bottom of the hill. The coefficient of kinetic Friction on the hill is 0.40. What is the coefficient of kinetic friction between the horizontal surface And the sled?

It requires 0.30 kJ of work to fully drive a stake into the ground. If the average resistive force on the stake by the ground is 828 N, how long is the stake?

How much kinetic energy does a 0.30-kg stone have if it is thrown at 44 m/s?

A 0.12-kg block is held in place against the spring by a 35-N horizontal external force. The external force is removed, and the block is projected with a velocity $v _ { 1 } = 1.2 \mathrm {~m} / \mathrm { s }$ when it separates from the spring, as shown in the figure. The block descends a ramp and has a velocity $v _ { 2 } = 1.4 \mathrm {~m} / \mathrm { s }$ bottom of the ramp. The track is frictionless between points A and B. The block enters a rough section at B, extending to E. The coefficient of kinetic friction between the block and the rough surface is 0.26 . The block moves on to D, where it stops. By how many centimeters was the spring initially compressed?

A girl throws a stone from a bridge. Consider the following ways she might throw the stone. The speed of the stone as it leaves her hand is the same in each case. Case A: Thrown straight up. Case B: Thrown straight down. Case C: Thrown out at an angle of 45° above horizontal. Case D: Thrown straight out horizontally. In which case will the speed of the stone be greatest when it hits the water below if there is no Significant air resistance?

Assuming negligible friction, what spring constant (force constant) would be needed by the spring in a "B-B gun" to fire a 10-g pellet to a height of 100 m if the spring is initially compressed by 0.10 M?

In a physical fitness program, a woman who weighs 510 N runs up four flights of stairs in 22 s. Each flight rises 3.1 m. (1 hp = 746 W) (a) What is her total change in potential energy? (b) What was the minimum average power (in watts) that she expended during the 22 s? (c) What horsepower motor would be required to generate the same power?

A 100%-efficient engine is being used to raise a 89-kg crate vertically upward at a steady rate. If the power output of the engine is 1620 W, how long does it take the engine to lift the crate a vertical distance of 18.7 m? Friction in the system is negligible.

The figure shows a famous roller coaster ride. You can ignore friction. If the roller coaster leaves point Q from rest, what is its speed at the top of the 25-m peak (point S)?

You do 116 J of work while pulling your sister back on a fritctionless swing, whose chain is 5.10 m long, until the swing makes an angle of 32.0° with the vertical. What is your sister's mass?

A very light ideal spring with a spring constant (force constant) of 2.5 N/cm pulls horizontally on an 18-kg box that is resting on a horizontal floor. The coefficient of static friction between the box and the floor is 0.65, and the coefficient of kinetic friction is 0.45. (a) How long is the spring just as the box is ready to move? (b) If the spring pulls the box along with a constant forward velocity of 1.75 m/s, how long is the spring? (c) How long is the spring if it pulls the box forward at a constant 2.75 m/s?

When you drop a pebble from height H, it reaches the ground with kinetic energy K if there is no air resistance. From what height should you drop it so it will reach the ground with twice as much Kinetic energy?

On an alien planet, an object moving at 4.0 m/s on the horizontal ground comes to rest after traveling a distance of 10 m. If the coefficient of kinetic friction between the object and the surface Is 0.20, what is the value of g on that planet?