Name (LAST, First) ______, ______
Date ___ / ___ / ______Block 1 2 3 4 5 6 7 8
Kinematics Review and Force Problems:
Work the following problems. The number in parenthesis preceding each problem is a reference for the teacher. The number(s) following some problems are answers. These answers do not necessarily have the correct number of significant digits. Drawing a free-body [force] diagram may help.
1. (5.33) You drive a car for 2.0 h at 40 km/h, then for another 2.0 h at 60 km/h.
- What is your average velocity? (50)
- Do you get the same answer if you drive 100 km at each of the two speeds?
Show your work. (No.)
2. (5.49) A plane uniformly accelerates from 66 m/s to 88 m/s in 12.0 s. Determine:
- The displacement of the plane while accelerating. (920)
- The acceleration of the plane. (2)
- The force exerted on a 72.5 kg passenger. (130)
3. (5.58) Rocket-powered sleds are used to test the responses of humans to acceleration. Starting from rest, one sled can reach a speed of 444 m/s in 1.80 s and can be brought to a stop again in 2.15 s. Assume the sled has a passenger with mass of 65 kg.
- Calculate the acceleration while the sled is speeding up. (250)
- Compare this starting acceleration to the acceleration due to gravity by determining the ratio [as a decimal, not a fraction] R = a/g. (25)
- Calculate the force exerted on the passenger by the sled. (2x104)
- Calculate the force exerted on the sled by the passenger.
- Repeat the above calculations for the period when the sled is slowing down. (-200, 20)
- Determine the displacements of the sled during both intervals. (400, 500)
4. (6.23) A 65 kg swimmer jumps off of a 10.0 m tower. The swimmer comes to a stop 2.0 m below the surface. Determine the:
- Swimmer’s velocity on hitting the water. (-14)
- Acceleration of the swimmer while slowing in the water. (+50)
- Net force on the swimmer by the water while slowing. (+4000)
- Time intervals during both accelerations. (1.4, 0.3)
5. (6.30) A horizontal force of 30.0 N is required to slide a 12.0 kg wooden crate across the floor at a constant velocity.
Hint: review http://www.physicsclassroom.com/Class/newtlaws/U2L2b.html
Determine the magnitude and direction of the:
- Gravitational force on the crate. (-200)
- Normal force exerted by the floor on the crate. (+200)
- Applied force on the crate. (30)
- Net force on the crate. (0)
Hint: http://www.physicsclassroom.com/Class/newtlaws/U2L2d.html - Frictional force exerted by the floor on the crate.
Calculate the:
- Acceleration of the box while moving? (0)
- Coefficient of kinetic friction between the crate and floor. (0.255)
6. (6.37) A sled of mass 50.0 kg is pulled along flat, snow-covered ground. The static friction coefficient is 0.30, and the kinetic friction coefficient is 0.10. Calculate or determine the following:
- The weight of the sled. (500)
- The minimum force required to start the sled moving. (150)
- The minimum force required to keep the sled moving at a constant velocity. (50)
- Once moving, what total force must be applied to the sled to accelerate it at a rate of 3.0 m/s/s? (200)
- At what rate will the sled accelerate if the force required to start the sled moving [static] is applied while the sled is moving [kinetic]? (2)
7. (6.39) A 65 kg boy and a 45 kg girl use an elastic rope while engaged in a tug-of-war on an icy, frictionless surface. The girl accelerates toward the boy at 3.0 m/s/s [relative to the ground]. Determine the:
- Force exerted by the girl on the rope. (135)
- Force exerted by the rope on the girl.
- Force exerted by the boy on the rope.
- Force exerted by the rope on the boy. (135)
- Magnitude of the acceleration [relative to the ground] of the boy toward the girl. (2.0)
- Magnitude of the acceleration [relative to the girl] of the boy toward the girl. (5.0)
- Weight of the girl. (440)
- Weight of the boy.
- Normal force on the girl.
- Normal force on the boy. (600)
The smooth, icy surface is replaced with a rough, icy surface. The coefficient of static friction is 0.24. Assume that the force(s) applied by the girl and boy remain constant.
- Calculate the friction force exerted on the girl’s feet by the icy surface.
- Will the girl move? Explain. Work is required.
- Will the boy move? Explain. Work is required.
The coefficient of kinetic friction is one-half the value of the coefficient of static friction. Assume that the force(s) applied by the girl and boy remain constant.
- Calculate the coefficient of kinetic friction. (0.12)
- Calculate the kinetic frictional force on both the boy and girl. (76, 53)
- Calculate the acceleration of the girl, relative to the ground. (1.8)
- Calculate the acceleration of the boy, relative to the ground. (0)
- A passing skater nudges the boy with enough force to break him free from the ice. Calculate his acceleration. (< 1)
Intro Problems (PPP) v07.doc 9/22/2008 1:13:00 PM Page 1 of 2