Question 1 (All basic physics).(adsbygoogle = window.adsbygoogle || []).push({});

A crane drops a 0.3 kg steel ball onto a steel plate. The ball's speeds just before impact and after are 4.5 m/s and 4.2 m/s, respectively.If the ball is in contact with the plate for 0.03 s, what is the magnitude of the average force that the ball exerts on the plate during impact.

Equations I thought would be useful (Basic Physics):

F=ma

a=v/t

My ATTEMPT at the question:

Well first i took my givens which were:

Mass of Ball: 0.3 kg

Velocity Before impact: 4.5 m/s

Velocity After impact: 4.2 m/s

Accelration of gravity constant: 9.8 m/s^2 (^2=squared[Exponential value as it is written on a calculator)

So my thinking is that we should find the easiest force equation there, being the first one (before impact):

F1=ma

F1=(0.3)x(9.8)

F1=2.94N (Newtons)

Then the second one (after impact):

F2=ma

F2=(0.3)a

(Finding acceleration)a=v/t

a=(4.2-4.5)/(0.03)

a=-3m/s^2

(Back to Force of second equation)

F2=(0.3)x(-3)

F2=-3N(Newtons)

So now i assume that force is a scalar quantity and thus negatives don't really apply, only the value so i use:

ƩF=Average Force=(F1+F2)/2

ƩF=(3+2.94N)/2

ƩF=(5.94N)/2

ƩF=2.97N and the multiple choice answers are:

(a) 3.0N (MY ANSWER SINCE I ROUNDED 2.97N TO 3.0N)

(b) 87N

(c) 3.5N

(d) 30N

(e) 133N

So I ask is how my answer (which was wrong) is not correct, where i messed up, what formulas i should have used, and what the correct answer is. (Note: This isn't homework it is a quiz question that i took and i never understood how it was wrong.)

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Energy and Momentum Physics Questions

**Physics Forums | Science Articles, Homework Help, Discussion**