A box of mass 10 kg sits on a cart with the usual low-frictionwheels. Someone pu
ID: 1674701 • Letter: A
Question
A box of mass 10 kg sits on a cart with the usual low-frictionwheels. Someone pushes it with a constant force of 20 N for 5seconds, but then loses contact with the box which heads into abrick wall. It takes much less than 5 seconds for the box tocome to a stop when it collides with the wall - suppose it takes0.1 seconds for the box to stop. Find the average force bythe wall on the box during that collision. I am confused about where to begin, don't know what to do withall of the information. A box of mass 10 kg sits on a cart with the usual low-frictionwheels. Someone pushes it with a constant force of 20 N for 5seconds, but then loses contact with the box which heads into abrick wall. It takes much less than 5 seconds for the box tocome to a stop when it collides with the wall - suppose it takes0.1 seconds for the box to stop. Find the average force bythe wall on the box during that collision. I am confused about where to begin, don't know what to do withall of the information.Explanation / Answer
The problem must be divided in two parts, when the cart is pushedand when it stops. This problem also supposes that the mass of thecar is meaningless. Step 1: Analysis of the cart when is pushed. --------------------------- We have the information F = 20 N, t = 5 s , m = 10 kg andv0= 0 and we have the formula for impact and momentum Ft= mvf - mv0. (20 N)(5 s) = (10 kg)vf - (10kg)(0) (Plugging the data in the formula) 100 N s = (10 kg)(vf) vf = 10 m/s Therefore the cart departs from a velocity of 10 m/s Step 2: Analysis of the cart when stops ------------------ Now we have t = 0.1 s, m= 10 kg, vo = 10 m/s (from thelast step) and vf = 0 m/s (the cart stops). Applying thesame formula we have, F(0.1 s) = (10 kg)(0 m/s) - (10 kg)(10 m/s) (Plugging the data into the formula) 0.1 F = - 100 N-s (Simplifying) F = - 1000 N (Solving for F) The force is negative because it stops the cart and goes againstmovement. So, the force required to stop the cart is 1000 N.
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