Question

1. A father has twice the mass of his son. At the beginning of a race, they are both running at 4.0 m/s. By the end of the race, both the father and the son have the same kinetic energy. If the father traveled at the same speed the entire race, what was the son’s change in speed?
2. A 2.0 kg box starts at rest on a flat, frictionless sheet of ice. A steady Texas wind then exerts on the box the force
� ⃑ = (230 N)�̂−(110 N)�̂, given in unit- vector notation, where the x direction is east and the y direction is north. In response to this force, and as a result of a frictionless rock ledge that constrains the box’s direction of motion, the box ends up with a displacement of 5.0 meters east and 2.0 meters north.
(a) How much work did the wind do during this displacement?
(b) If all the work done on the box became kinetic energy, what was the final speed of the box?

3. You are designing a one-car rollercoaster ride. The car and rider have a combined mass of 210 kg. At the end of the ride, the car emerges onto a horizontal, straight section of track with an initial speed of 45 m/s. A steady braking force along this section of track then brings the car to stop after it has traveled 35 m.
(a) What is the magnitude of the braking force?
(b) What is the magnitude of the acceleration of this car while the force is applied?
(c) What is the acceleration of this car in terms of g-factor (i.e. how many multiples of 9.8 m/s2)?
4. A crane lifts a 220 kg piano from the ground to the top of a 25 m high building for a rooftop concert. How much work did the crane do on the piano to accomplish this? (The piano experienced no net gain in kinetic energy.)
5. A catapult at a fair is used to chuck watermelons. The catapult’s spring has a spring constant of 300 N/m. If the spring is stretched 1.8 m away from its relaxed position when the catapult is pulled back and set for launch, then how much work is needed to set the catapult for launch?
6. The force on a particle is directed along the x axis and given by the expression:
F = Ax2 where A is a known constant. How much work is done on the particle by the force in moving it from x = 1 to x = 2?

Answer 1