Question 78: Motion in 2D & Vectors

Question

At t = 0, truck, starting from rest, moves in the positive x-direction at uniform acceleration of 5 ms
$$-$$2
. At t = 20 s, a ball is released from the top of the truck. The ball strikes the ground in 1 s after the release. The velocity of the ball, when it strikes the ground, will be :
(Given g = 10 ms
$$-$$2
)

Accepted Answer

At t = 20 s,
velocity of truck,
v = 0 + 5 $$	imes$$ 20 = 100 m/s
At 20 sec a ball is dropped from the truck, so velocity of ball will be same as truck.
Velocity of truck at x-direction = 100 m/s and in y-direction = 0.
$$	herefore$$ Velocity of ball v
x
= 100 m/s, v
y
= 0
Now ball will show projectile motion where vertically downward acceleration g = 10 m/s act on the ball.
As horizontally no acceleration acting on the ball so horizontal velocity 100 m/s will remain unchanged.
Velocity of the ball when it reach the ground along y-direction after 1 sec.
$${v_y} = 0 - 10 	imes 1$$
$$\Rightarrow$$ $${v_y} =  - 10$$ m/s
$$	herefore$$ Velocity of ball $$(\overrightarrow v ) = 100\widehat i - 10\widehat j$$

Answer

$$100\widehat i - 10\widehat j$$

Answer

$$10\widehat i - 100\widehat j$$

Answer

$$100\widehat i$$

Answer

$$ - 10\widehat j$$

Motion in 2D & Vectors

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