Download Homework 3 3.1 A spacecraft that is initially at rest

Homework 3
3.1 A spacecraft that is initially at rest turns on its engine at t = 0. If its mass is m = 3000 kg and
the force from the engine is 45 N, what is the acceleration of the spacecraft?
3.2 A hockey puck moves on an icy surface that is frictionless, with a constant speed of 30 m/s.
How long does it take the puck to travel the length of the hockey rink (60 m)?
Homework 3
3.11 An object with an initial velocity of 12 m/s accelerates uniformly for 25 s. (a) If the final
velocity is 45 m/s, what is the acceleration? (b) How far does the object travel during this time?
Homework 3
3.30 Two books of mass m1 = 8 kg and m2 = 5.5 kg
are stacked on a table as shown in the figure below.
Find the normal force acting between the table and
the bottom book.
Homework 3
Homework 3
3.36 Three blocks rest on a frictionless, horizontal table (see figure below),
with m1 = 10 kg and m3 = 15 kg. A horizontal force F = 110 N is applied to
block 1, and the acceleration of all three blocks is found to be 3.3 m/s2. (a)
Find m2. (b) What is the magnitude of the normal force between blocks 2 and
3?
Homework 3
Homework 3
3.43 You are trying to slide a refrigerator across a horizontal floor. The mass of the refrigerator
is 200 kg, and you need to exert a force of 350 N to make it just begin to move. (a) What is the
coefficient of static friction between the floor and the refrigerator? (b) After it starts moving, the
refrigerator reaches a speed of 2.0 m/s after 5.0 s. What is the coefficient of kinetic friction
between the refrigerator and the floor?
Homework 3
Homework 3
3.47 A hockey puck slides along a rough, icy surface. It has an initial velocity of 35 m/s and
slides to a stop after traveling a distance of 95 m. Find the coefficient of kinetic friction between
the puck and the ice.
Homework 3
3.48 A rock is dropped from a very tall tower. If it takes 4.5 s for the rock to reach the ground,
what is the height of the tower?
Homework 3
3.61 A crate of mass 55 kg is attached to one end of a string, and the other
end of the string runs over a pulley and is held by a person as in the figure
below. If the person pulls with a force of 85 N, what is the crate's
acceleration? (Assume that upward is the positive direction. Indicate the
direction with the sign of your answer.)
Homework 3
3.63 You work for a moving company and are given the
job of pulling two large boxes of mass m1 = 120 kg and m2
= 290 kg using ropes as shown in the figure below. You
pull very hard, and the boxes are accelerating with a = 0.22
m/s2. What is the tension in each rope? Assume there is no
friction between the boxes and the floor.
Homework 3
3.72 Calculate the terminal velocity for a baseball. A baseball's diameter is approximately d =
0.070 m, and its mass is m = 0.14 kg. Express your answer in meters per second and miles per
hour. (Assume a drag coefficient of 1 and air density of 1.3 kg/m3.)