A ball is attached to the end of a 16 m string and it

Question

1. An 5 kg grinding disk has a diameter of 54 cm and is rotating at 650 rev/min. What braking force must be applied tangentially to the disk if it is to stop rotating in 5 s?
2. A 540 g steel rod 40 cm in length is pivoted about its center and rotated at 300 rev/min. What is the angular momentum(kg·m/s²)?
3. A 1000 kg car travels at a constant speed of 12 m/s along a circular track. If the centripetal acceleration is 9 m/s², what is the radius of the track(m)?
4. A 60 g firecracker explodes, sending a 50 g piece to the left and the other to the right with a velocity of +40 m/s. What is the velocity of the 50 g piece(m/s)?
5. A 28 kg girl and a boy on roller skates stand at rest facing each other. They push each other as hard as they can, and the boy moves to the left with a velocity of 3 m/s, while the girl moves to the right with a velocity of 1 m/s. What is the mass of the boy?
6. A 50 kg mass is lifted a vertical distance of 28 m in a time of 2 s. What average power was employed(Kw)?
7. A ball is attached to the end of a 1.6 m string, and it swings in a circle with a constant speed of 6 m/s. What is the centripetal acceleration(m/s²)?