Chapter 4 Laws of Motion Homework Problems
1) Find the weight of a body whose mass is:
a. 3 kg
b. 200 g
2) A 20 kg object that can move freely is subjected to a resultant force of 45 N in the negative x-direction. Find the
acceleration of the object.
3) A 5.0 kg object is to be given an upward acceleration of 0.30 m/s2 by a rope pulling straight upward on it. What
must the tension be in the rope?
4) A horizontal force of 140 N is needed to pull a 60 kg box across the horizontal floor at a constant speed. What is
the coefficient of friction between the floor and box?
5) The only force acting on a 5 kg object has components Fx = 20 N and Fy = 30 N. Find the acceleration of the
object.
6) A 600 N object is to be given an acceleration of 0.70 m/s2 How large an unbalanced force must act upon it?
7) A constant force acts on a 5 kg object and reduces its velocity from 7 m/s to 3 m/s in a time of 3 s. Find the
force.
8) A 400 g block with an initial velocity of 80 cm/s slides along a horizontal tabletop against a friction force of 0.70
N.
a. How far will it slide before stopping?
b. What is the coefficient of friction between the block and the tabletop?
9) A 600 kg car is moving on a level road at 30 m/s.
a. How large a retarding force (assumed to be constant) is required to stop it in a distance of 70 m?
b. What is the minimum coefficient of friction between the tires and the roadway if this is to be possible?
10) An 8000 kg engine pulls a 40 000 kg train along a level track and gives it an acceleration of a1 = 1.20 m/s2. What
acceleration, a2, would the engine give to a 16 000 kg train?
11) A force acts on a 2 kg mass and gives it an acceleration of 3 m/s2 What acceleration is produced by the same
force when acting on a mass of:
a. 1 kg
b. 4 kg
c. How large is the force?
12) An object has a mass of 300 g
a. What is its weight on earth?
b. What is its mass on the moon?
c. What will be its acceleration on the moon when a 0.50 N resultant force acts on it?
13) A horizontal cable pulls a 200 kg cart along a horizontal track. The tension in the cable is 500 N. Starting from
rest:
a. How long will it take the cart to reach a speed of 8 m/s?
b. How far will it have gone?
14) A 900 kg car is going 20 m/s along a level road. How large a constant retarding force is required to stop it in a
distance of 30 m. (Hint: first find its acceleration.)
15) A 900 kg car is going 20 m/s along a level road. How large a constant retarding force is required to stop it in a
distance of 30 m? (Hint: first find its deceleration.)
16) A 12.0 kg bullet is accelerated from rest to a speed of 700 m/s as it travels 20 cm in a gun barrel. Assuming the
acceleration to be constant, how large was the accelerating force? (Be careful of units.)
17) A 20 kg crate hangs at the end of a long rope. Find its acceleration when the tension in the rope is:
a. 250 N
b. 150 N
c. Zero
d. 196 N
18) Using the scale described the problem above, a 65 kg astronaut weighs himself on the moon, where g=1.60
m/s2. What does the scale read?