Question

 

A monkey sits on a bathroom scale which is on the floor of an elevator for a very tall building. The monkey has a mass of 42.0 kg. What is the reading on the scale if there is not motion and no acceleration? When the elevator starts moving the scale reads 480 N. Describe the acceleration for this case. At another time the scale reads 360 N. Describe the acceleration for this second case. Calculate the acceleration in each case.  

A car collides with a fence in such a manner as to cause the fence to bend by 0.330 m. The car was initially traveling at a speed v = 26.0 m/s but it comes to a complete stop. Determine the acceleration for someone in the car. What force had to be exerted on someone in the car?

Answer 1

If there is not motion and no accelaration

Fnet = 0

reading on the scale is 42*9.8 = 411.6 N

if the scale reads 480 N

Fnet = 480-411.6 = 68.4 N

m*a = 68.4

accelaration a = 68.4/42 = 1.63 m/s^2

if the scale reads 360 N

Fnet = 360-411.6 =-51.6 N

accelaration a = -51.6/42 = -1.22 m/s^2

2) initial velocity is u = 26 m/sec

final velocity is v = 0 m/sec

distance trav elled before coming to rest is s = 0.33 m

then using v^2 - u^2 = 2*a*s

0^2-26^2 = 2*a*0.33

accelaration a = -1024.24 m/s^2

using work energy theorem w = 0.5*m*u^2

F*s = 0.5*m*u^2

F*0.33 = 0.5*m*26^2

F = 1024.24*m

m is the mass of the car