Physics Problems Flashcards
A bike accelerates uniformly from rest to a speed of 7.10 m/s over a distance of 35.4 m. Determine the acceleration of the bike?
0.712 m/s2
A bullet with a mass of 0.02 kg leaves a gun at 500 m/s.
If the gun’s mass is 2 kg, what is the velocity of the recoil on the gun?
The correct answer is: 5 m/s
momentum of bullet = mass × velocity
= 0.02 kg x 500 m/s
= 10 kg m/s
Rearrange the equation: velocity = momentum ÷ mass velocity of recoil on gun = 10 kg m/s ÷ 2 kg
= 5 m/s
A 25 kg bicycle is travelling at 12 m/s. What force is needed to bring it to a halt in 5 s?
The correct answer is: 60 N
Momentum at start = 25 × 12 = 300 kg m/s
Momentum at end = 0 × 12 = 0 kg m/s
Change in momentum = 300 - 0 kg m/s
Force = Change in momentum / time taken for change
Force = 300 / 5 = 60 N
A 804 kg drag race car accelerates from rest to 113 km/h in 1.1 s. What average force is exerted on the car?
The correct answer is: 22942.42 N
Force = change in momentum / time taken
113 km/h = 31.39 m/s
804 x 31.39 = 25236.67 kg-m/s
25236.67/1.1 = F = 22942.42 N
If a car with a mass of 1000 kg moves at 20 m/s. What braking force is needed to bring the car to a halt in 10s?
The correct answer is: 2000 N
Momentum at start = 1000 × 20 = 20000 kg m/s
Momentum at end = 0 x 20 = 0 kg m/s
Change in momentum = 20000 - 0 kg m/s
Force = Change in Momentum 20000 / time taken 10 = 2000 N
A physics teacher has a weight of 800N. If his feet have an area of 0.025 square metres each, what pressure does he exert on the ground?
The correct answer is: 16,000 Pa (Remember, he has two feet!)
If a car has a mass of 800 kg and moves with a velocity of 25 m/s, what force is needed to stop the car in 50 metres?
The correct answer is: 5000 N
To answer this question we need to calculate how much kinetic energy the car has before we can calculate how much force is needed to stop the car.
Kinetic Energy = 05 x mass x velocity2
= 0.5 × 800 × 252
= 05 × 800 × 625
= 250,000J.
Energy = Force x Distance
The equation can be rearranged to give
Force = Energy ÷ Distance = 250,000 ÷ 50
= 5,000 N.
The force needed to stop the car in 50 metres is 5,000 N
Tom has a circuit with 4 resistors in parallel. The first resistor is 1 ohm, the second resistor is 2 ohms the third resistor is 3 ohms and the forth resistor is 6 ohms. Find the total resistance of this circuit?
The correct answer is: 0,5 ohm
1/Re = 1/R1 + 1/R2 + 1/R3 + 1/R4
Abal si thrown verticaly upwards from hte ground at avelocity fo12. ms/. Approximately, how long does ti atke ot reach hte ground again?
5 seconds
2 seconds
2.5 seconds
1.25 seconds
2.5 seconds
Name the general mode of heat transfer in
a) Solids
b) Liquids and gases
(a) The general mode of heat transfer in solids is conduction.
(b) The general mode of heat transfer in liquids and gases is convection.
What is Convection of Heat? Give an example.
Heat is transferred from a higher temperature region to a lower temperature region in liquids and gases during this process. Convection heat transfer occurs partly due to molecular movement and partly as a result of mass transfer.
Define Radiation. Give an example.
It is the method of transferring heat from one body to another without engaging the medium’s molecules. Radiation heat transfer does not rely on the medium.
For example: In a microwave, the substances are heated directly without any heating medium.
Heat transfer takes place according to which of the following law?
a) Newton’s second law of motion
b) First law of thermodynamics
c) Second law of thermodynamics
d) Newton’s law of cooling
c) Second law of thermodynamics
Which of the following is the rate of heat transfer unit?
Watt
A person prefers to sit by a fire during the cold winter months. Which of the following heat transfer types gives him the most heat?
a) Radiation will provide quick warmth
b) Convection and radiation together
c) If it is near the fire, convection sounds good
d) Conduction from the fire
a) Radiation will provide quick warmth
