Physics Homework Ch4

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1. A football punter accelerates a football from rest to a speed of 13 m/s during the time in which his toe is in contact with the ball (about 0.24 s). If the football has a mass of 0.50 kg, what average force does the punter exert on the ball?
 __________ N

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2. A 11.0-kg object undergoes an acceleration of 2.9 m/s².
a). What is the magnitude of the resultant force acting on it?
_________ N
b). If the same force is applied to a 22.0-kg object, what acceleration is produced?
________ m/s².




3. One or more external forces are exerted on each object enclosed in a dashed box shown in the figure below. Identify the reaction to each of these forces. (Assume that (a), (b), and (c) occure on Earth while (d), (e), and (f) occur far from any outside gravitational influences. Select all that apply).

A)	The spring exerts a force		B)	The wagon exerts a force
□	downward on the Earth		□	downward on the Earth due to contact
□	to the right on the hand		□	upward on the Earth due to contact
□	upward on the Earth		□	downward on the Earth due to gravitational attraction
□	to the right on the wall		□	downward to the left on the handle
□	to the left on the hand		□	upward on the Earth due to gravitational attraction
□	to the left on the wall		□	upward to the left on the handle
C)	the ball exerts a force		D)	m exerts a force
□	downward to the left on the player		□	to the left on M
□	upward to the right on the player		□	to the right on M
□	downward on the Earth		□	upward on M
□	downward to the right on the player		□	downward on M
□	upward on the Earth
E)	-q exerts a force		F)	The iron exerts a force
□	to the right on Q		□	downward on the magnet
□	upward on Q		□	upward on the magnet
□	to the left on Q		□	to the left on the magnet
□	downward on Q		□	to the right on the magnet

4. A bag of sugar weighs 6.00 lb on Earth. What would it weigh in newtons on the moon, where the free-fall acceleration is one-sixth that on Earth?
________N

Repeat for Jupiter, where g is 2.64 times that on Earth.
________N

Find the mass of the bag of sugar in kilograms at each of the three locations
Earth ____ kg
Moon ____kg
Jupiter____kg




5. A freight train has a mass of 1.3 X 10⁷ kg. If the locomotive can exert a constant pull of 7.4 X 10⁵ N, how long does it take to increase the speed of the train from rest to 78 km/h?
_________min



6. A 73-kg man standing on a scale in an elevator notes that as the elevator rises, the scale reads 842 N. What is the acceleration of the elevator?
_____m/s² upward.




7. A 5.6-g bullet leaves the muzle of a rifle with a speed of 320 m/s. What force (assumed constant) is exerted on the bullet while it is traveling down the 0.75-m-long barrel of the rifle?
______N



8. A boat moves through the water with two forces acting on it. One is a 1,500-N forward push by the water on the propeller, and the other is an 1,200-N resistive force due to the water around the bow.
a). What is the acceleration of the 800-kg boat?

b). If it starts from rest, how far will the boat move in 5.0 s?
______m

c). What will its velocity be at the end of that time?
________m/s





9. A 891-kg car starts from rest on a horizontal roadway and accelerates eastward for 5.00 s when it reaches a speed of 30.0 m/s. What is the average force exerted on the car during this time?
_______N eastward





10. A 2.00 kg block is held in equilibrium on an incline of angle θ = 65° by a horizontal force  applied in the direction shown in the figure below. If the coefficient of static friction between block and incline is μ_s = 0.300, determine the following.

a). The minimum value of 
________ N
b). the normal force exerted by the incline on the block
________N

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11. Consider the figure below.















a). Find the tension in each cable supporting the 700-N cat burglar. (Assume the angle θ of the inclined cable is 32.0° )
Inclined cable        ________N
Horizontal Cable   ________N
Vertical Cable       ________N

b). Suppose the horizontal cable were reattached higher up on the wall. Would the tension in the inclined cable
__increase,
__decrease,
__or stay the same?




12. The leg and cast in the figure below weigh 347 N(w₁). Determine the weight w₂ and angle α needed so that no force is exerted on the hip joint by the leg plus cast.
w₂ = _______ N
α =  _________ °






13. A crate of mass m = 25 kg rides on the bed of a truck attached by a cord to the back of the cab as in the figure. The cord can withstand a maximum tension of 63 N before breaking. Neglecting friction between the crate and truck bed, find the maximum acceleration the truck can have before the cord breaks.
_______m/s²












14. Two packing crates of masses m₁ = 10.0 kg and m₂ = 4.00 kg are connected by a light string that passes over a frictionless pulley as in the figure. The 4.00-kg crate lies on a smooth incline of angle 34.0°















a). Find the acceleration of the 4.00-kg crate.
________m/s²  (up the incline)

b). Find the tension in the string
_________ N

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15. Assume the three blocks (m₁ = 1.0 kg, m₂ = 2.0 kg, and m₃ = 4.0 kg) portrayed in the figure below move on a frictionless surface and a force F = 44 N acts as shown on the 4.0-kg block.







a) determine the acceleration given this system
 ________m/s² (to the right)

b). Determine the tension ion the cord connecting the 4.0-kg and the 1.0-kg blocks
________N

c). Determine the force exerted by the 1.0-kg block on the 2.0-kg block.
_________N





16. A block of mass m = 5.3 kg is pulled up a θ = 26° incline as in the figure with a force of magnitude F = 33 N.

a). Find the acceleration of the block if the incline is frictionless

b). Find the acceleration of the block if the coefficient of kinetic friction between the block and the incline is 0.12
________m/s²





17. A dockworker loading crates on a ship finds that a 17-kg crate, initially at rest on a horizontal surface, requires a 73-N horizontal force to set in motion. However, after the crate is in motion, a horizontal force of 52 N is required to keep it moving with a constant speed. Find the coefficient of static and kinetic friction between the crate and floor.
μ_{static _______}μ_{kinetic ______}






18. In the figure below, m₁ = 9.5 kg and m₂ = 3.5 kg. The coefficient of static friction between m_{1 and the horizontal surface is 0.5, and the coefficient of kinetic friction is 0.30.}

















a) If the system is released from rest, what will its acceleration be?
_________m/s²b) If the system is set in motion with m₂ moving downward, what will be the acceleration of the system?
________m/s²










19. A 1,400-N crate is being pushed across a level floor at a constant speed by a force  of 330 N at an angle of 20.0° below the horizontal, as shown in the figure (a) below.

a). What is the coefficient of kinetic friction between the crate and the floor?
μ_k = ________

b). If the 330-N force is instead pulling the block at an angle of 20.0° above the horizontal, as shown in the figure (b), what will be the acceleration of the crate?
Assume that the coefficient of friction is the same as that found in part (a).
_________m/s²






20. The coefficient of static friction between the m = 3.30-kg crate and the 35.0° incline of the figure below is 0.295. What minimum force  must be applied to the crate perpendicular to the incline to prevent the crate from sliding down the incline?
_________N