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Chapter 4
1. A CD is ejected from a computer. The CD has a mass of 0.2kg. What is
the force on the CD if it is accelerated at 1.4m/s2?
2. An elevator is pulled upward with a force of 5000lb from a cable. The
elevator weighs 3000 lbs. What if the total force on the elevator?
3. What is the acceleration of the elevator in the previous problem?
4. The ABS (Antilock Brake System) on a car is based on the principle that
the coefficient of starting friction is greater than sliding friction. The
coefficient of starting friction for rubber on wet concrete is 1.5, the
coefficient of sliding friction for rubber on wet concrete is 0.97. How many
times faster can a car stop using ABS versus locking up the brakes?
5. A robotic arm with a mass of 75kg starts from rest and accelerates till it
reaches a speed of 2.0m/s in 3.0seconds. What is the final momentum of the
arm?
6. What was the force on the arm in the previous problem?
7. As a CD is ejected from a computer the computer recoils backward in
order to conserve momentum. If the computer has a mass of 10kg, the CD a
mass of 0.2kg and is ejected at a speed of 2.0m/s, what is the recoil speed of
the computer?
8. A weight scale is made using a force sensor that has an output of
10mV/Lb. If 25Lb is added to the scale how many mV does the sensor put
out?
9. A force is applied to the scanning arm inside a copy machine moving the
arm across the page it is scanning. If the arm starts from rest, has a mass of
2.0kg and reaches a speed of 0.4m/s in a time of 0.8s, what was the net force
on the arm?
10. An I.C. chip is inserted into a socket. The chip is pushed downward with
a force of 0.1Lb. The socket has friction resisting the chips insertion with a
force of 0.04Lb. If the chip weighs 1.0 Oz ( 16 Oz = 1Lb) what is its
acceleration into the socket? Remember to convert weight into mass!
11. A computer weighing 12Lb is sitting on a table. If the table is to support
the computer what force must the table exert upward on the computer?
12. A motor weighs 2Lb, what is its mass?
13. A solenoid pulls in its plunger with a mass of 0.13slugs with a force of
2.0Lb, what is the acceleration of the plunger?
14. When adding a lubricant to a surface the coefficient of sliding friction
dropped from 0.4 to 0.3. If without the lubricant it took 10Lb of force to
slide an object over the surface, what is the force required with the
lubricant?
15. Another name for starting friction is static friction, it is the frictional
force that is needed to budge a static or stationary object. If a power supply
weighing 22Lb is to be slid across a table where the coefficient of starting
friction is 0.5, how much force is needed to budge the supply?
16. An elevator weighing 2000Lb is pulled upward with a force of 2100Lb.
What is the acceleration of the elevator?
17. A shopping cart weighing 55Lb gets away from a shopper heading for a
stack of cans at a speed of 2.5ft/s. What is the momentum of the cart?
18. A conveyer belt starting from rest transports a box of mass 15kg to a
speed of 0.4m/s in 2.0s. What force was applied to the box?
19. A doorbell consists of a solenoid with a plunger that moves in and out
striking a bell. The plunger has a mass of 0.3kg and is ejected at 2.1m/s. The
solenoid has a mass of 1.2kg. What is the recoil velocity of the solenoid?
20. Two men are trying to push a piece of equipment weighing 100Lb. One
mean pushes with 50Lb the other with 40Lb. The coefficient of starting
friction is 0.35. How fast does the piece of equipment accelerate?