PHYSICS HOMEWORK 4
Science

Tutor: None Selected  Time limit: 0 Hours 
1. At a given instant in time, a 14kg rock that has been dropped from a high cliff experiences a force of air resistance of 40 N. What are the magnitude and direction of the acceleration of the rock? (Do not forget the gravitational force!)
magnitude ________ m/s?
direction _____downward/upward_____?
2. A 7.0kg block being pulled across a table by a horizontal force of 55 N also experiences a frictional force of 10 N. What is the acceleration of the block?
_______ m/s2?
3. An upward force of 45 N is applied via a string to lift a ball with a mass of 2.5 kg.
(a) What is the net force acting upon the ball?
magnitude __________?
direction __downward/upward________?
(b) What is the acceleration of the ball?
magnitude ________?
direction __upward/downward?
Acceleration due to gravity = 9.8m/s2 (10m/s2 could be used to simplify numbers)
1) Force = mass*acceleration
For rock
F = 14kg * 9.8m/s2 = 137.2 N
Deduct air resistance.
137.2  40 = 97.2N
Acceleration of rock.
acceleration = Force/mass
A = 97.2/14 = 6.94 m/s2 downward
2) again F=m*a
total force = 5510 =45 N (horizontal force resistance)
a = 45/7 = 6.43m/s2
a) F=m*a = 2.5*9.8 = 24.5 N
Resultant force = 4524.5 = 20.5 N upward
b) a = F/m = 20.5/2.5 = 8.2 m/s2 upwards
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