A person who normally weighs 300N stands on a scale and jumps upward. When doing

Question

A person who normally weighs 300N stands on a scale and jumps upward. When doing this a person notices that the scale momentarily reads 400N. Calculate the the person's acceleration during this jump. a = 3.3m/s^2 A book sits on top of a car that is initially at rest, then suddenly the car starts to accelerate. If the static coefficient of friction between the top of the car and the book is 0 45, what is the maximum acceleration the car can have before the book starts to slide. Assume the car accelerates in a straight line. a = 4.41 m/s^2

Explanation / Answer

2.) Weight = mass x gravity

So, 300 = mass x 9.81 => mass = 300 /9.81 = 30.581039 kg

the normal reading of the scale is because of the weight of the person. The additional reading (400 - 300 = 100 N) is due to the jump. So, the force that the person applied on the scale while jumping is 100 N.

And hence the acceleration during this jump is = force applied / mass = 100 / 30.581039 = 3.27 ~ 3.3 m/s2  

3.) The frictional force between the book and the car is the only thing that accelerates the book.

Maximum friction = mg   

and hence the maximum acceleration = maximum friction / mass = mg / m = g = 9.81 x 0.45 = 4.4145 m/s2

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