A.) A 14 kg block is at rest on a level floor. A 420 g glob of putty is thrown a
ID: 1389497 • Letter: A
Question
A.) A 14 kg block is at rest on a level floor. A 420 g glob of putty is thrown at the block such that it travels horizontally, hits the block, and sticks to it. The block and putty slide 15 cm along the floor. If the coefficient of sliding friction is 0.40, what is the initial speed of the putty?
_____m/s
B.) William Tell shoots an apple from his son's head. The speed of the 140-g arrow just before it strikes the apple is 29.1 m/s, and at the time of impact it is traveling horizontally. If the arrow sticks in the apple and the arrow/apple combination strikes the ground 7.1 m behind the son's feet, how massive was the apple? Assume the son is 1.85 m tall.
_____g
Explanation / Answer
A)
The velocity of the block and the putty as they slide 15 cm along the floor must first be determined before the initial velocity of the putty can be calculated.
Vf^2 - V^2 =2as
s = distance travelled by putty and block before stopping = 15 cm = 0.15 m. (given)
The acceleration of the block and the putty is,
a = - (?k * g)
where
?k = coefficient of friction = 0.4 (given)
g = acceleration due to gravity = 9.8 m/sec^2 (constant)
Hence,
a = - 0.4 * 9.8 = - 3.92 m/sec^2 --- the negative sign attached to the acceleration implies that the block and putty were slowing down as they were skidding to a stop.
Substituting appropriate values in Equation 1,
0 - V^2 = 2(-3.92)(0.15)
V^2 = 1.176
V = 1.08 m/sec.
MbVb + MpVp = (Mb + Mp)(1.08)
where
Mb = mass of the block = 14 kg (given)
Vb = initial velocity of block = 0 (at rest)
Mp = mass of putty = 420 g = 0.42 kg (given)
Vp = initial velocity of putty
Substituting values,
14(0) + 0.42(Vp) = (14.42)(1.08)
Solving for Vp,
Vp = 37.08 m/sec.
B)
Marr*Varr=(Marr+Mapp)V2
The goal here is to solve for Mapp, but we also have the unknown V2.
(y-yo)=Vo*t+.5*a*t^2 , but Vo=0 so,
(y-yo)= .5*a*t^2 solving for t yields: t=sqrt(2*(y-yo)/g)
t=.614 seconds
(x-xo)=V2*t+.5*a*t^2
V2=((x-xo)-.5*g*t^2)/t
V2=8.55 m/s
Mapp=((Marr*Varr)/V2)-Marr
Mapp=0.336kg
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.