Units & Motion
List 4 fundamental quantities
length
time
mass
amount of substance
luminous intensity
temperature
current
State Newton's first law
An object at rest remains at rest and an object in motion remains in motion at a constant speed unless acted upon by an external force
What is the angular displacement in radians of an object 7.5 cm from the center of a rotating disc as it traces out an arc length of 12.3 cm
θ = s/r = 12.3 cm/ 7.5 cm = 1.64 rad
What is the absolute zero point?
0 Kelvin or -273°C
Temperature at which all the heat energy has been removed from any substance
Theoretically the lowest temperature an object can reach
What is the SI BASE unit of force
F = ma = kgm/s2
Calculate the mass of an object that requires a force of 50 N to accelerate the 2.5 m/s2
F = ma
m = F/a = 50 N/2.5 m/s2 = 20 kg
What is the angular velocity of a wheel that rotates with an angular displacement of 4/8 rad in 4 mins?
ω = θ/t = 4.8 rad /(4x60s) = 0.02 rad/s
List 2 types of thermometers
thermocouple
gas thermometer
liquid-in-glass thermometer
clinical thermometer (digital or analogue)
Calculate the deceleration of a cyclist moving from speed of 25 m/s to 5 m/s in 10s
a = v-u/t = 5m/s - 25 m/s/ 10s = -2m/s2
A force of 50 mN is applied 60 m away from the pivot, what is the moment of the force?
T = Fd = (50/1000 N)(60m) = (0.05N)(60m) = 3 Nm
A helicopter of mass 2000kg is at a height of 350 m above the Earth. What is the gravitational potential energy in MJ? Use g as 10 m/s2
GPE = mgh = (2000kg)(350m)(10m/s2)
= 7,000,000 J
= 7 MJ
Determine the amount of heat energy to convert a block of mass 4kg from 20° C to 60° C. Specific heat capacity = 400 J/kgK. Give answer in kJ
E = mcΔT = (4kg)(400 J/kgK)(40K) = 64000 J = 64 kJ
A car accelerates at 4 m/s2 from rest. Calculate the distance traveled after 1200 ms (to 3 sf)
s = ut + (1/2) at2
= (0x1.2 s) + (1/2)(4m/s2)(1.2)2
= 2.88 m
Two children of mass 45 kg and 50 kg respectively. The 45 kg child collides with a speed of 5 m/s with the 50 kg child at rest. The 45kg child moves away with a speed of 8m/s. What is the final velocity of the 50 kg child.
Pbefore = Pafter
m1u1 + m2u2 = m1v1 + m2v2
(45 kg)(5m/s) + (50kg)(0m/s) = (45kg)(8m/s) + (50kg)v2
225 kgm/s = 360 kgm/s + 50v2
225-360)kgm/s = 50v2
v2 = -137 kgms-1 /50 kg = -2.7 m/s
A tank has an energy input of 3.5 kW. Determine the efficiency if the tank exerts 200 J of energy in 0.2 s
Power input = 3.5 kW = 3500 W
Power output = E/t = 200J/0.2 s = 1000W
Eff = Pout/Pin x 100 = 1000W/3500W x 100 = 28.6%
Two resistors P and Q are connected in series. The circuit is supplied with a 12 V battery. P = 6Ω and Q = 4Ω
What is the Power through Q?
Total I = V/R = 12V/10Ω = 1.2 A
P = I2R = (1.2)2(4Ω ) =5.76 W
OR
V = IR = (1.2A)(4Ω) = 4.8V
P = V2/R = (4.8V)2/(4Ω ) =5.76 W
OR
P = IV= (1.2A)(4.8V) = 5.76W