A wood block, after being given a starting push, slides down a ramp at a constant speed. what is the angle of the ramp above horizontal? suppose that μk = 0.35.


Answer 1

The solution for the problem is:

Constant speed means Fnet = 0. 
Let m = mass of wood block and Θ = angle of ramp; then if µk = 0.35 …

The computation would be:

Fnet = 0 = mg (sin Θ) - (µk) (mg) (cos Θ) 
mg (sin Θ) = µk (mg) (cos Θ) 
µk = tan Θ 
Θ = arctan(µk)

= arctan (0.35)

≈ 19.3°

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An object is travelling with a constant acceleration of 10 ms⁻² . how much distance will it travel in 3rd second of its journey?



Acceleration is uniform and acceleration (a) = 10 m/s^2

Now it has been mentioned for the first 2 secs the acceleration is 10m/s^2 .

Hence velocity= acceleration x time

Velocity= 10 x 2 = 20 m/s

Consider s as the distance traveled in the 3rd second.

Now we know s= ut+1/2(at^2)

Where s is the distance measured in m.

u is the initial velocity measured in m/sec

t is the time taken for the object to travel the above distance. This is equal to one second as we need to calculate the distance traveled between 3rd and 2nd second.

t = (3-2)= 1 sec

Substituting the given values in the above formula we get

s = 20 x1 + 1/2 (10 x 1 x 1)

s = 25 m

Thus the distance traveled by the object in the 3rd second is 25 m


A 16 g rifle bullet traveling 240 m/s buries itself in a 3.6 kg pendulum hanging on a 2.5 m long string, which makes the pendulum swing upward in an arc. Determine the vertical and horizontal components of the pendulum's displacement.



x = 0.54 m

y = 0.058 m


m = mass of the bullet = 16 g = 0.016 kg

v = speed of bullet before collision = 240 m/s

M = mass of the pendulum = 3.6 kg

L = length of the string = 2.5 m

h = height gained by the pendulum after collision

V = speed of the bullet and pendulum combination

Using conservation of momentum

m v = (m + M) V

(0.016) (240) = (0.016 + 3.6) V

V = 1.062 m/s

Using conservation of energy

Potential energy gained by bullet and pendulum combination = Kinetic energy of bullet and pendulum combination

(m + M) g h = (0.5) (m + M) V²

(9.8) h = (0.5) (1.062)²

h = 0.058 m

y = vertical displacement = h = 0.058 m

x = horizontal displacement

horizontal displacement is given as

x = sqrt(L² - (L - h)²)

x =  sqrt(2.5² - (2.5 - 0.058)²)

x = 0.54 m


Which best identifies the requirements for work to be performed? A) An object that has a force acting on it.
B) An object that is moving and has no net force
C) A force acting on a motionless object
D) A force that moves an object


D. a force that moves an object
It would be choice D (a force that moves an object)

A linear accelerator uses alternating electric fields to accelerate electrons to close to the speed of light. A small number of the electrons collide with a target, but a large majority pass through the target and impact a beam dump at the end of the accelerator. In one experiment the beam dump measured charge accumulating at a rate of -2.0 nC/s. How many electrons passed through the accelerator over 1.8 hours?



8.1 x 10^13 electrons passed through the accelerator over 1.8 hours.


The total charge accumulated in 1.8 hours will be:

Total Charge = I x t = (-2.0 nC/s)(1.8 hrs)(3600 s/ 1 hr)

Total Charge = - 12960 nC = - 12.96 x 10^(-6) C

Since, the charge on one electron is e = - 1.6 x 10^(-19) C

Therefore, no. of electrons will be:

No. of electrons = Total Charge/Charge on one electron

No. of electrons = [- 12.96 x 10^(-6) C]/[- 1.6 x 10^(-19) C]

No. of electrons = 8.1 x 10^13 electrons

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