4-A 5-kg box sits on a 10-kg box in an elevator. Discuss the forces and accelera
ID: 1659003 • Letter: 4
Question
4-A 5-kg box sits on a 10-kg box in an elevator. Discuss the forces and accelerations of each box when the elevator is (i) stationary, (i) moving upwards with constant speed, (ili) speeding up while moving upwards, (iv) slowing down while moving upwards. 5- You are at a party with helium-filled balloons attached to strings on the tables. One balloon has detached, and is touching the ceiling. A friend at the about party knows you are taking physics and asks you the forces on the balloon that is touching the ceiling. You estimate each balloon to have a mass of 10 g and holds 14 g of helium; knowing a little about electrostatics, you determine that the balloon is attracted to the ceiling with 0.20-N of electrostatic force. Explain to your friend whether there is a normal force on the balloon. 6-Zach, whose mass is 80 kg, is in an elevator descending at 10 m/s. The elevator takes 3.0 s to brake to atop at the first floor a) What is Zach's weight before the elevator start braking? b) What is Zach's weight while the elevator is barking?Explanation / Answer
4 i) When elevator is stationary , net force on both the boxes is zero, accelerations are zero as well.
The weight of the 5kg box is balanced by normal force by bigger box. The weight and normal force by the smaller box is balanced by normal force by elevators floor.
ii) When elevator is moving with constant speed , net force on both the boxes is zero, accelerations are zero as well.
The weight of the 5kg box is balanced by normal force by bigger box. The weight and normal force by the smaller box is balanced by normal force by elevators floor.
iii) In this case both the boxes have upward accelerations. Net force is also upward on both of them.
The normal on smaller box by bigger box is more than smaller box's weight. The normal from elevators floor on bigger box is more than its weight+normal by small box.
iv) In this case , the net force on both boxes is downward.
Their upward acceleration is negative or we can say they are accelerating downward.
The weight of small box is more than normal reaction by bigger box. And the weight of bigger box + normal by smaller box is more thann normal by floor.
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