JEE Main · 2021 · 26 Aug 2021 · Shift 1 · Kinematics

WhatsApp Email

Two spherical balls having equal masses with radius of 5 cm each are thrown upwards along the same vertical direction at an interval of 3s with the same initial velocity of

35 m / s

, then these balls collide at a height of ______ m. (Take

g = 10 m / s^{2}

)

Answer: 50

Solution

Measuring time from the first throw, the heights of the two balls are

h_{1} = 35 t - 5 t^{2}, h_{2} = 35 (t - 3) - 5 (t - 3)^{2}

Equating them,

35 t - 5 t^{2} = 65 t - 150 - 5 t^{2}

30 t = 150

and

t = 5

s, which is inside the

7

s flight time of the first ball. The common height is

h = 35 (5) - 5 (5)^{2} = 175 - 125 = 50 m

The two balls meet

50

m above the point of projection; their

5

cm radii shift this by less than a tenth of a metre.

JEE Main · 2021 · 26 Aug 2021 · Shift 1 · Integer answer

Practise more: all JEE Main PYQs on Kinematics →

More JEE Main questions on Kinematics

A projectile is thrown upward at an angle $6 0^{\circ}$ with the horizontal. The speed of the projectile is 20 m/s when its direction of motion is $4 5^{\circ}$ with the horizontal. The initial speed of the projectile is ______ m/s.
JEE Main 2026View solution →
A river of width 200 m is flowing from west to east with a speed of $18 km / h$ . A boat, moving with speed of $36 km / h$ in still water, is made to travel one-round trip (bank to bank of the river). Minimum time taken by the boat for thi …
JEE Main 2026View solution →
An object is projected with kinetic energy K from a point A at an angle $6 0^{\circ}$ with the horizontal. The ratio of the difference in kinetic energies points B and C to that at point A (see figure), in the absence of air friction is :
JEE Main 2026View solution →
A block is sliding down on an inclined plane of slope $θ$ and at an instant $t = 0$ this block is given an upward momentum so that it starts moving up on the inclined surface with velocity $u$ . The distance $(S)$ travelled by the block before its velocity become zero, …
JEE Main 2026View solution →
A paratrooper jumps from an aeroplane and opens a parachute after 2 s of free fall and starts deaccelerating with $3 m / s^{2}$ . At 10 m height from ground, while descending with the help of parachute, the speed of paratrooper is …
JEE Main 2026View solution →
A bead $P$ sliding on a frictionless semi-circular string $(A C B)$ and it is at point $S$ at $t = 0$ and at this instant the horizontal component of its velocity is $v$ . Another bead $Q$ of the same mass as $P$ is ejected from point $A$ at $t = 0$ …
JEE Main 2026View solution →