Work and Kinetic Energy of baseball

AI Thread Summary
To calculate the work required to throw a baseball at 90 mph, the equation W = (change) KE, where KE = 1/2 mv^2, is used. The baseball weighs 5 oz, which needs to be converted correctly to mass in slugs for accurate calculations. The conversion from miles per hour to feet per second is also necessary. The correct answer, as stated in the calculus book, is 85.1 ft-lbs, which highlights the importance of proper unit conversions in physics problems. The initial confusion was resolved by converting the weight of the ball to its mass using gravitational acceleration.
saraleigh117
Messages
2
Reaction score
0
How many foot pounds of work does it take to throw a baseball 90 mph? A baseball weighs 5 oz, or 0.3125 lb.

The only equation I can find is W= (change) KE, where KE=1/2mv^2

When I try plugging in the data given I'm not getting the correct answer. I don't know if I'm doing incorrect unit conversions or what. This is actually in my calculus book physics but this seemed like the more appropriate place to post the question. By the way, the answer in the book is 85.1 ft-lbs. Please help me. I'm dyin' over here.
 
Physics news on Phys.org
You have the right equation, so you must be doing your conversions incorrectly, which is a little tough in the USA units when mass comes into play. You must first convert miles/hr to ft/sec, and pounds to slugs per m=W/g.
 
Post your calculations.
 
Nevermind, I've got it. I didn't convert the weight of the ball to the mass of the ball using the gravitational acceleration. Thanks.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

The average force needed to throw a baseball 90mph?
Replies
5
Views
5K
How Does Kinetic Energy Change in a Baseball After Being Hit?
Replies
9
Views
5K
Work energy KE theorem for a book being lifted up in a gravitional field
Replies
18
Views
2K
Work done during a collision -- Change in Kinetic Energy & change in Momentum
Replies
1
Views
2K
Finding kinetic energy and initial velocity of a cart over time
Replies
6
Views
2K
Work and kinetic energy comprehension question
Replies
4
Views
2K
Potential energy and conservation of energy problem
Replies
1
Views
2K
Calculating Kinetic Energy in English Units
Replies
1
Views
15K
Angular Momentum & Moment Of Inertia
Replies
8
Views
3K
Projectile Motion : Work and Energy
Replies
4
Views
1K

Hot Threads

Recent Insights

Back
Top