Physical Science Review
29. The Difference between Velocity and Acceleration
Velocity is the speed rate that is measured in one instant, while acceleration is the measurement of speed change. For example, a truck if a truck is traveling 20 kilometers per one hour, then its velocity is 20km/hr but of the truck driver puts their foot down and the truck starts to speed up, the truck experiences acceleration.
34. Rabbit’s Average Speed
The speed is the distance/time so, since there is a given distance and a time, then
speed = 30m/2s = 30/2 m/s = 15m/s.
36. Hamster’s Acceleration
0 m/s 0 seconds
5 m/s 1 second
10 m/s 2 seconds
40. Net force produced by 30-N and 20-N force in cases (a) both forces act same direction and (b) two forces on different directions.
An astronaut of weight 120 kg recedes from the spacecraft by switching a small propulsion unit attached to his back. The force being generated by a gas is 30 N. Show that his acceleration is 0.25 m/s2
44. Scaffold’s Weight
The right hand scale reads 700 N
48. Tennis ball speed
- average speed = distance moved / time taken, therefore, average speed = 24 / 0.5 = 48 m/s.
- Air resistance is encountered as the ball's shape interacts with the air it passes through, which slows down the travel time.
78. Pushing the carton horizontally
The friction between the carton and the floor increases as the gravity was added up to the pushing force.
88. Absence of air resistance
- The speed of the ball would decrease by 9.8 m/s. 9.8m/s is the rate of any object in free fall
- In absence of air resistance the ball would drop with acceleration because of gravity
- when we throw the ball vertically up , the time of ascent will be equal to the time of descent
100. Harry’s early vacation
In Harry's everyday method of hanging from the bosun's chair, the rope pulls up on Harry along with two forces so each force only one-half Harry's weight and that is only 250 N that is why the rope breaks and he fell down.
106. Balls A and B
Ball B will reach the track first because it gains extra speed that made it overall higher average speed on track B
40. Astronaut’s Acceleration
F = m.a
30N = 120kg.a
30N
a = --------
120kg
=0.25m/s2
44. Rocket Mass
100,000 kg × 2 m/s2 = 200,000 N.
60. Your empty hand is not hurt when it bangs lightly against a wall
Based on the firstlaw, for the moving bag tendsto continue moving, which squashes the hand.
64. Pulling a wagon
Law is the law of inertia that states an object at rest or motion will stay at rest or motion unless another force acts upon it.
66. Tossing a coin upward
Its velocity slows down and the acceleration lowers down due to gravity.
72. Action and reaction forces
- action is the force applied by hammer
reaction is the nail applies an equal in magnitude but opposite direction
- action is the gravity that is pulling the book
reaction is the book pulling the ground up
- the action is when the blade is pushing the air downwards
reaction is when the air is pushing the helicopter up
88. Mack truck and Motorcycle
Based on Newton’s third law, the force will be the same magnitude. But the force's effect or the acceleration will not be the same for each due of the different mass. The more massive truck will undergo less change in motion than the motorcycle
98. Ball rolling down with decreasing acceleration and increasing speed
Only on hill B will have acceleration along the pathdecrease with time, because hill becomes less steep as the motion progresses. When the hill levels off, acceleration will be zero. On hill A, acceleration is constant. On hill C, acceleration increases asthe hill becomes steeper. In all three cases, speed increases.
110. Dropping a pair of tennis ball
The ball that is filled with lead pellets will fall first as it has more weight that makes the gravity pull stronger. The ball that falls faster will also have the greater air resistance as it has more speed than the other one.
