General Physics Final Exam Questions 1. A 0.05 kg bullet is fired horizontally i

Question

General Physics Final Exam Questions


1. A 0.05 kg bullet is fired horizontally into a 8.0-kg block of wood suspended by a rope from the ceiling. The block swings in an arc, rising 0.03 m in height above its lowest position. What was the speed of the bullet?

The answer is 123 m/s.
Why? Please explain step by step.



2. During the design of a loop-the-loop on a roller coaster, the designer wants to have a 75.0-kg small car just barely touching the track at the top of a loop that has a 15.0-m radius. What should be the minimum speed at the top of the loop?

The answer is 12.1 m/s.
Why? Please explain step by step.


Thanks.

Explanation / Answer

1. lets v be speed of the block after being hit by the bullet. mv^2/2=mgh (conservation of energy) so v^2=2gh so v=0.77(m/s). let V be speed of the bullet. conservation of momentum. V*0.05=(0.05+8)*v so V=123(m/s) 2.at the top of the loop, there are three forces act on the car. normal of the ray (downward) centripetal force (upward) gravitational force (downward). so mv^2/r=N+mg for the car just barely touching the ray, N=0. so v=sqrt(rg)=12.1(m/s)

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