Introductory Physics 1 - Test 3 (Work & Energy)

(25 kg)(9.8 m/s²)(2.4 m) - 1/2(25)(2.2 m/s)² 588 - 60.5 = 527.5 J

A 25 kg child slides down a 2.4-m-high playground slide. She starts from rest, and her speed at the bottom is 2.2 m/s. What is the change in the thermal energy of the slide and the seat of her pants?

mv²/2 = kx²/2 v = x√(k/m) = 30 × √(60000/15000) = 60 m/s

As a 15000 kg jet lands on an aircraft carrier, its tail hook snags a cable to slow it down. The cable is attached to a spring with spring constant 60000 N/m. If the spring stretches 30 m to stop the plane, what was the plane's landing speed?

vf² = 2m(b)gh / m(a) + m(b) = (2)(4 kg)(9.8)(0.50 m) / (12 + 4 kg) = 2.45 m²/s² vf = √2.45 = 1.56 m/s

Boxes A and B in (Figure 1) have masses of 12.5 kg and 4.0 kg , respectively. The two boxes are released from rest. Use conservation of energy to find the boxes' speed when box B has fallen a distance of 0.50 m. Assume a frictionless upper surface.

(55 × 10⁻⁸)(9.8)(0.40) = 2.16 × 10⁻⁶ J

Fleas have remarkable jumping ability. A 0.55 mg flea, jumping straight up, would reach a height of 40 cm if there were no air resistance. In reality, air resistance limits the height to 20 cm. What is the flea's kinetic energy as it leaves the ground?

potential energy

If you raise an object to a greater height, you are increasing its __________.

W = (120 N)(150 m) cos(0°) = 1.8 × 10⁴ J

Mark pushes his broken car 150 m down the block to his friend's house. He has to exert a 120 N horizontal force to push the car at a constant speed. How much thermal energy is created in the tires and road during this short trip?

a) W = (255 kg)(9.8 m/s²)(4 m)(cos (0°)) = 9996 J b) W(1) = (1830 N)(4 m)(cos(210°)) = -6339 J c) W(2) = (1295 N)(4 m)(cos(135°)) = -3663 J

The two ropes seen in (Figure 1) are used to lower a 255 kg piano exactly 4 m from a second-story window to the ground. a) How much work is done by w? b) How much work is done by T1? c) How much work is done by T2?

a) 500 × 4.7 × cos(180) = -2350 J b) 326 × 4.7 × cos(20) = 1439.80 J c) 223 × 4.7 × cos(30) = 907.68 J

The two ropes shown in the bird's-eye view of (Figure 1) are used to drag a crate 4.7 m across the floor. a) How much work is done by the force fk? b) How much work is done by the force T1? c) How much work is done by the force T2?

Moving a block of wood across a horizontal rough surface at constant speed.

W is the work done on the system, K, U, and Eth are the kinetic, potential, and thermal energies of the system, respectively. Any energy not mentioned in the transformation is assumed to remain constant; if work is not mentioned, it is assumed to be zero. Give a specific example of a system with the energy transformation shown. W→ΔEth

A wood block sliding across a rough horizontal surface and slowing to a stop.

W is the work done on the system, and K, U, and Eth are the kinetic, potential, and thermal energies of the system, respectively. Any energy not mentioned in the transformation is assumed to remain constant; if work is not mentioned, it is assumed to be zero. Select a specific example of a system with the energy transformation shown: K→ΔEth.

A wood block sliding down a rough inclined surface at a constant speed. In this case, the potential energy of the block is decreasing and getting converted into thermal energy. This transformation is U→ΔEth.

W is the work done on the system, and K, U, and Eth are the kinetic, potential, and thermal energies of the system, respectively. Any energy not mentioned in the transformation is assumed to remain constant; if work is not mentioned, it is assumed to be zero. Select a specific example of a system with the energy transformation shown: U→ΔEth.

h = (3.1 m)(sin(24°) = 1.26 m v = √2(9.8 m/s²)(1.26 m) = 4.97 m/s

What minimum speed does a 100 g puck need to make it to the top of a frictionless ramp that is 3.1 m long and inclined at 24°?